feat(sync): add SyncLegacyCosignTags config to skip syncing legacy cosign/SBOM tags when disabled

[andaaron]

1. Add SyncLegacyCosignTags config to skip syncing legacy cosign/SBOM tags when disabled
2. Sync on demand with referrers API should not use recursion to sync referrers of referrers
3. Add tests SyncLegacyCosignTags and changes in /referrers on demand sync.

Credit for the tests goes to @jzhn see, https://github.com/project-zot/zot/pull/3840/changes

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 88.63636% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.46%. Comparing base (bb121c3) to head (6eb02a9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/extensions/sync/service.go	88.09%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3842   +/-   ##
=======================================
  Coverage   91.45%   91.46%           
=======================================
  Files         193      194    +1     
  Lines       27456    27464    +8     
=======================================
+ Hits        25111    25121   +10     
+ Misses       1521     1520    -1     
+ Partials      824      823    -1     

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[Copilot]

Pull request overview

This PR adds a SyncLegacyCosignTags sync configuration flag to optionally skip syncing legacy cosign/SBOM digest-encoded tags, and adjusts on-demand referrer syncing so it does not recursively sync referrers-of-referrers. It also introduces tests covering the new flag and the updated /referrers on-demand behavior.

Changes:

• Add SyncLegacyCosignTags to sync config (defaulting to true) and thread it into sync logic to skip legacy tag syncing when disabled.
• Change on-demand SyncReferrers to call referrer syncing in non-recursive mode.
• Add/extend tests for legacy-tag syncing and non-recursive on-demand referrer syncing.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkg/extensions/sync/service.go	Gates legacy tag listing/sync behind SyncLegacyCosignTags and adds a recursive flag to referrer syncing so on-demand can be non-recursive.
pkg/extensions/sync/sync_test.go	Adds end-to-end tests for SyncLegacyCosignTags and on-demand /referrers non-recursive behavior.
pkg/extensions/sync/sync_internal_test.go	Updates internal tests for new syncReferrers signature and adds unit tests asserting legacy-tag behavior and non-recursive on-demand behavior.
pkg/extensions/config/sync/config.go	Adds SyncLegacyCosignTags config field and helper ShouldSyncLegacyCosignTags() defaulting to true when unset.
pkg/extensions/config/sync/config_test.go	Adds tests for ShouldSyncLegacyCosignTags() default/true/false behavior.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

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