T7334: pr mirror trigger workflow added with label creation permission for default github token

[kumvijaya]

Change summary

In pr mirror trigger workflow, In the very first run, had to create the mirror-initiated label manually.
The vyos bot user used in PR mirror trigger workflow currently doesn't have permission to create label

As this label has to be created in current repo, the default GitHub action workflow token can do this.
So, adding the required permissions for this workflow.

This updated pr mirror trigger workflow with label creation permission

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/T7334

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

[c-po]

Add write permissions for PRs