Improve shell completion for docker secret and docker config subcommands

[thaJeztah]

remove redundant closures around completion functions

These were remnants from some earlier implementation.

cli/command/secret: remove completion for "ls"

This command takes no arguments, so should not provide completion.

cli/command/secret: fix completion to complete names, not IDs

cli/command: fix completion for secret create, config create

These commands accept two arguments; the first is a custom name,
the second is either a filename or "-" to create from STDIN.

With this patch:

# does not provide completion
docker secret create <tab>

# starts providing completion once a non-empty name is provided
docker secret create somename<tab>
file.txt other-file.txt

- What I did

- How I did it

- How to verify it

- Human readable description for the release notes

Improve shell completion for `docker secret` and `docker config` subcommands.

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/config/create.go	0.00%	15 Missing ⚠️
cli/command/secret/create.go	0.00%	15 Missing ⚠️
cli/command/secret/cmd.go	0.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[thaJeztah]

Interesting failure;

--- FAIL: TestGetAutoPAT (0.00s)
    --- FAIL: TestGetAutoPAT/general_error (0.00s)
        api_test.go:388: assertion failed: expected error to contain "unexpected response from Hub: 500 Internal Server Error", got "Post \"http://127.0.0.1:49229/v2/access-tokens/desktop-generate/\"": net/http: HTTP/1.x transport connection broken: http: CloseIdleConnections called"

[thaJeztah]

Thx! I had a couple other PRs related to completions (and some other bits) open as well; if you have time to have a peek.