Add migrate repo archiver and packages storage support on command line

[lunny]

This PR also introduce generics syntax of Go1.18 and merged many iterate functions as one.
Fix #20566

[wxiaoguang]

The space => tab change looks strange to me (is it required by the new linter?)

Otherwise LGTM except the question below.

Already updated, LGTM again.

[KN4CK3R]

Please update this too and the docs if there any:

	Flags: []cli.Flag{
		cli.StringFlag{
			Name:  "type, t",
			Value: "",
			Usage: "Kinds of files to migrate, currently only 'attachments' is supported",
		},

[lunny]

@wxiaoguang test added.
@KN4CK3R All done. And find there is a tmp directory under package storage directory. It maybe not suitable. An OS tmp directory or a Gitea global special tmp directory maybe better.

[KN4CK3R]

That's automaticaly added:

gitea/modules/storage/local.go

Lines 51 to 53 in 2b4d43d

	if config.TemporaryPath == "" {
	config.TemporaryPath = config.Path + "/tmp"
	}

[codecov-commenter]

Codecov Report

Merging #20757 (233e02d) into main (86c85c1) will increase coverage by 0.01%.
The diff coverage is 15.87%.

@@            Coverage Diff             @@
##             main   #20757      +/-   ##
==========================================
+ Coverage   47.03%   47.04%   +0.01%     
==========================================
  Files         987      988       +1     
  Lines      136398   136352      -46     
==========================================
- Hits        64154    64151       -3     
+ Misses      64361    64318      -43     
  Partials     7883     7883              

Impacted Files	Coverage Δ
models/db/iterate.go	0.00% <0.00%> (ø)
models/git/lfs.go	25.90% <ø> (+2.53%)	⬆️
models/repo/attachment.go	53.38% <ø> (+6.72%)	⬆️
models/repo/repo_list.go	78.80% <ø> (+3.13%)	⬆️
models/user/search.go	87.83% <ø> (+16.40%)	⬆️
routers/private/mail.go	0.00% <0.00%> (ø)
services/repository/avatar.go	36.00% <0.00%> (ø)
cmd/migrate_storage.go	5.76% <15.38%> (+5.76%)	⬆️
modules/packages/content_store.go	100.00% <100.00%> (ø)
modules/process/manager_exec.go	86.04% <0.00%> (-6.98%)	⬇️
... and 4 more

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[lunny]

make L-G-T-M work.