T7644: mirror workflow refactoring rollout

[kumvijaya]

Change summary

🛠️ Mirror Refactoring Rollout

The mirror setup has been streamlined to simplify onboarding and maintenance:

✅ Changes Implemented

• Consolidated the mirror logic into a single workflow within the source repository.
• Removed the PR mirror trigger workflow.
• Removed the temporary feature branch cleanup workflow.
• Eliminated usage of the REMOTE_REPO variable.

🎯 Benefits

• Reduces Onboarding overhead, Reduces complexity and potential setup errors.
• No need for initial manual execution or temporary branch creation in the target organization.
• Reduces multiple workflows management in source and target org.

🧹 With this change, the following are removed:

1. PR mirror trigger workflow.
2. Head branch cleanup workflow.
3. PR mirror workflow in the target repository.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://vyos.dev/T7644

Related PR(s)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

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[c-po]

Enable new pr-mirror workflow tested in vyos-1x

[dmbaturin]

Let's get the new workflow in.