Onboard new inter-branch merge flow [Workflow]

[f-alizada]

Context

Onboarding new merge flow based on the github actions

Changes Made

Added github workflow for the branch.

References Documentation https://github.com/dotnet/arcade/blob/main/Documentation/Maestro/New-Inter-Branch-Merge-Approach.md One pager: https://github.com/dotnet/dnceng/blob/main/Documentation/OnePagers/github-action-inter-branch-merge.md

[wtgodbe]

Only the main branch is active in this repo, so inter-branch merges are no longer needed - closing