Add merge-mate actions

[ianhattendorf]

https://github.com/gitkraken/merge-mate-action

Closes https://github.com/gitkraken/vscode-gitlens-private/issues/80

[augmentcode]

🤖 Augment PR Summary

Summary: Adds GitKraken Merge Mate GitHub Actions workflows to automate PR branch syncing and apply/undo conflict resolutions.

Changes:

• Introduces Merge Mate Sync workflow to run on main updates (and manually) and sync eligible PRs via gitkraken/merge-mate-action/sync
• Introduces Merge Mate Review workflow to process apply/undo operations via PR comment edits or manual workflow_dispatch
• Configures required write permissions and OIDC (id-token: write) for the action to authenticate
• Passes GitKraken AI provisioner token for AI-assisted conflict resolution and filters PRs (targeting main, updated within 7 days)

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[augmentcode]

Review completed. 3 suggestions posted.

Comment augment review to trigger a new review at any time.

[eamodio]

I'd suggest adding Augments guard, and then run prettier pnpm run pretty to fix the formatting.