cli/command: Reapply "remove uses of GetAuthConfigKey, ParseRepositoryInfo" and add test

[thaJeztah]

cli/command: add unit-test for RetrieveAuthTokenFromImage

It's currently slower because it calls registry.ParseRepositoryInfo,
which does a DNS lookup for hostnames to determine if they're a loopback
address (and marked "insecure");

go test -v -run TestRetrieveAuthTokenFromImage
=== RUN   TestRetrieveAuthTokenFromImage
=== RUN   TestRetrieveAuthTokenFromImage/no-prefix
=== RUN   TestRetrieveAuthTokenFromImage/docker.io
=== RUN   TestRetrieveAuthTokenFromImage/index.docker.io
=== RUN   TestRetrieveAuthTokenFromImage/registry-1.docker.io
=== RUN   TestRetrieveAuthTokenFromImage/registry.hub.docker.com
=== RUN   TestRetrieveAuthTokenFromImage/[::1]
=== RUN   TestRetrieveAuthTokenFromImage/[::1]:5000
=== RUN   TestRetrieveAuthTokenFromImage/127.0.0.1
=== RUN   TestRetrieveAuthTokenFromImage/localhost
=== RUN   TestRetrieveAuthTokenFromImage/localhost:5000
=== RUN   TestRetrieveAuthTokenFromImage/no-auth.example.com
--- PASS: TestRetrieveAuthTokenFromImage (0.35s)
    --- PASS: TestRetrieveAuthTokenFromImage/no-prefix (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/docker.io (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/index.docker.io (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/registry-1.docker.io (0.08s)
    --- PASS: TestRetrieveAuthTokenFromImage/registry.hub.docker.com (0.12s)
    --- PASS: TestRetrieveAuthTokenFromImage/[::1] (0.13s)
    --- PASS: TestRetrieveAuthTokenFromImage/[::1]:5000 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/127.0.0.1 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/localhost (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/localhost:5000 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/no-auth.example.com (0.01s)
PASS
ok  	github.com/docker/cli/cli/command	1.367s

Reapply "cli/command: remove uses of GetAuthConfigKey, ParseRepositoryInfo"

This reverts commit f596202, and reapplies
79141ce.

cli/command: remove uses of GetAuthConfigKey, ParseRepositoryInfo

Re-implement locally, based on the code in github.com/docker/docker/registry,
but leaving out bits that are not used on the client-side, such as
configuration of Mirrors, and configurable insecure-registry, which
are not used on the client side.

This commit contains a regression due to a typo in authConfigKey;

const authConfigKey = "https:/index.docker.io/v1/"

Which is missing a / after the scheme.

Which currently fails the TestRetrieveAuthTokenFromImage test.

cli/command: fix regression in resolving auth from config

This was introduced in 79141ce, which
was reverted in f596202, and re-applied
in the previous commit.

Before this patch, saving credentials worked correctly;

docker login -u thajeztah
Password:
Login Succeeded

cat ~/.docker/config.json
{
	"auths": {
		"https://index.docker.io/v1/": {
			"auth": "REDACTED"
		}
	}
}

But when resolving the credentials, the credentials stored would not be found;

docker pull -q thajeztah/private-test-image
Error response from daemon: pull access denied for thajeztah/private-test-image, repository does not exist or may require 'docker login': denied: requested access to the resource is denied

With this patch applied:

docker pull -q thajeztah/private-test-image
docker.io/thajeztah/private-test-image:latest

Thanks to @mtrmac (Miloslav Trmač) for spotting this mistake!

Note that this PR also improves performance, as no DNS lookups happen to determine
if the registry is a loopback (and "insecure");

go test -v -run TestRetrieveAuthTokenFromImage
=== RUN   TestRetrieveAuthTokenFromImage
=== RUN   TestRetrieveAuthTokenFromImage/no-prefix
=== RUN   TestRetrieveAuthTokenFromImage/docker.io
=== RUN   TestRetrieveAuthTokenFromImage/index.docker.io
=== RUN   TestRetrieveAuthTokenFromImage/registry-1.docker.io
=== RUN   TestRetrieveAuthTokenFromImage/registry.hub.docker.com
=== RUN   TestRetrieveAuthTokenFromImage/[::1]
=== RUN   TestRetrieveAuthTokenFromImage/[::1]:5000
=== RUN   TestRetrieveAuthTokenFromImage/127.0.0.1
=== RUN   TestRetrieveAuthTokenFromImage/localhost
=== RUN   TestRetrieveAuthTokenFromImage/localhost:5000
=== RUN   TestRetrieveAuthTokenFromImage/no-auth.example.com
--- PASS: TestRetrieveAuthTokenFromImage (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/no-prefix (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/docker.io (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/index.docker.io (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/registry-1.docker.io (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/registry.hub.docker.com (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/[::1] (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/[::1]:5000 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/127.0.0.1 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/localhost (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/localhost:5000 (0.00s)
    --- PASS: TestRetrieveAuthTokenFromImage/no-auth.example.com (0.00s)
PASS
ok  	github.com/docker/cli/cli/command	0.388s

- Human readable description for the release notes

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 53.33333% with 7 lines in your changes missing coverage. Please review.

Project coverage is 59.13%. Comparing base (b8034c0) to head (0e32baf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5969      +/-   ##
==========================================
+ Coverage   59.09%   59.13%   +0.03%     
==========================================
  Files         354      354              
  Lines       29733    29739       +6     
==========================================
+ Hits        17572    17587      +15     
+ Misses      11191    11178      -13     
- Partials      970      974       +4     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Benehiko]

let's hope this one doesn't get reverted :)

[thaJeztah]

@vvoland ptal 🤗

[thaJeztah]

Bringing this in; just was discussing with @vvoland if we wanted to squash the "fix the regression" commit with the "Reapply" commit (I kept it separate to make it more visible), because it could impact git bisect, but looks like git bisect may be smart enough to handle this if it steps through merge commits (not individual commits).

Let's hope that's the case indeed (otherwise blame me!)