api: cross-namespace policy target selectors

[guydc]

What type of PR is this?

What this PR does / why we need it:

• Adds the option to select targets across all namespaces
• Inspired by https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io/v1.RouteNamespaces
• In the future, we can extend this mechanism to support:
  • List of named namespaces
  • Label selector to select namespaces

Which issue(s) this PR fixes:

Relates to #5143

Release Notes: Yes/No

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.84%. Comparing base (d50be42) to head (ba7b099).
⚠️ Report is 1608 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5145      +/-   ##
==========================================
- Coverage   66.88%   66.84%   -0.05%     
==========================================
  Files         210      210              
  Lines       32998    32998              
==========================================
- Hits        22070    22056      -14     
- Misses       9589     9599      +10     
- Partials     1339     1343       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!

[zhaohuabing]

Should we have an enum member Same defined here?

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!