doc: add feature marks to cmd description and log

[qweeah]

What this PR does / why we need it:
This PR updates feature marks to commands and features as summarized below:

1. stable commands need to remove preview mark

• oras blob
  • oras blob fetch
  • oras blob delete
  • oras blob push
• oras manifest
  • oras manifest fetch
  • oras manifest fetch-config
  • oras manifest delete
  • oras manifest push
• oras repo
  • oras repo ls
  • oras repo tags
• oras cp

2. preview commands

• oras attach, oras discover: since the command always involves referrer API change, GA requires distribution-spec v1.1 release

3. experimental commands
   none

4. preview features

• --distribution-spec: oci distribution spec v1.1 is not released
• oras pull --include-subject: image with subject will be defined in oci image-spec v1.1
• oras cp --recursive: recursively upward lookup for referrers requires referrer API in oci distribution spec v1.1
• oras repo tags --exclude-digest-tags: it uses the tag scheme as fallback referrers API fallback and defined in oci distribution spec v1.1

5. experimental features

• --image-spec: uses artifact manifest
• oras repo tags: should print experimental hint when using associated tag/digest querying

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #860

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[yizha1]

@qweeah Are there any flags for oras repo tags: print when using associated tag/digest querying?

[qweeah]

@qweeah Are there any flags for oras repo tags: print when using associated tag/digest querying?

No, there is no flag. But when used, there will be a log output saying it's an experimental feature in verbose mode.

[codecov-commenter]

Codecov Report

Merging #865 (9296eaa) into main (03bc2b2) will not change coverage.
The diff coverage is 0.00%.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@           Coverage Diff           @@
##             main     #865   +/-   ##
=======================================
  Coverage   66.39%   66.39%           
=======================================
  Files          21       21           
  Lines         860      860           
=======================================
  Hits          571      571           
  Misses        243      243           
  Partials       46       46           

Impacted Files	Coverage Δ
cmd/oras/internal/option/spec.go	18.51% <0.00%> (ø)
cmd/oras/internal/option/target.go	18.75% <0.00%> (ø)

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[shizhMSFT]

LGTM

[yizha1]

LGTM but IANAM

[FeynmanZhou]

@qweeah What's the reason for making the following three commands to Preview status in v1.0.0?

oras pull --include-subject
oras cp --recursive
oras repo tags --exclude-digest-tags

[qweeah]

@qweeah What's the reason for making the following three commands to Preview status in v1.0.0?

oras pull --include-subject # image with subject will be defined in oci image-spec v1.1
oras cp --recursive # recursively upward lookup for referrers requires referrer API in oci distribution spec v1.1
oras repo tags --exclude-digest-tags # uses the tag scheme fallback defined in oci distribution spec v1.1

Basically, because the underlying specs are not released. Commented inline.

[FeynmanZhou]

Make sense. Agree with the changes above.

[TerryHowe]

LGTM

[shizhMSFT]

LGTM