feat: MAR-file Import

[ReneHezser]

Overview/Summary

A GitHub App, that has read permissions on the content of the MCR repository and another one, that can create a PR for this repository. This app already exists.

Scope	Name	Value
Repository Secret	MAR_REPO_ACCESS_APP_PRIVATEKEY	the multi-line private key, starting with SHA256
Repository Variable	MAR_REPO_OWNER	Microsoft
Repository Variable	MAR_REPO_REPOSITORY	MCR
Repository Variable	MAR_REPO_ACCESS_APPID	typically a 7-digit number
Repository Secret	APP_ID	already exists for other actions
Repository Secret	APP_SECRET	already exists for other actions

Testing

https://github.com/ReneHezser/Azure-Verified-Modules/actions/runs/23550887269/job/68564275018

This PR fixes/adds/changes/removes

Breaking Changes

None

As part of this Pull Request I have

• Read the Contribution Guide and ensured this PR is compliant with the guide
• Checked for duplicate Pull Requests
• Associated it with relevant GitHub Issues or ADO Work Items (Internal Only)
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Ensured PR tests are passing
• Updated relevant and associated documentation (e.g. Contribution Guide, Docs etc.)