Add required labels for all PRs (#2885)

## What is the purpose of the change

Subcomponent of #2088

This PR is pretty overdue, but is a first step in getting our PR management / backporting flow be far easier to manage. 

It requires all PRs to main to have a label indicating if its state machine compatible or breaking. We can then start making more automated security checks and backport tooling for these. This is done by using https://github.com/mheap/github-action-required-labels

The check re-runs after a label is applied!

E.g. 
* if backport
  * and merge conflicts, a bot opens a draft backport PRs that are kept in sync and we can conflicts on. 
  * If no conflicts, CI can show in PR status checks whether state machine compat passes. This can be used to guarantee state machine compatability guarantee pre-merge to main, and have the merge automatically cause a commit to the relevant release branch. 
* If SM compat, Simulator runs to check state machine compatible, etc.

## Testing and Verifying

This PR status check failed until I added the label.

## Documentation and Release Note

We likely need to add:
* Some docs to contributing.md 
* Perhaps a PR template update
* Perhaps a more informed error message

.github/workflows/required_labels.yml

@@ -0,0 +1,18 @@
+name: required labels
+
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled, synchronize]
+    branches:
+      - 'main'
+jobs:
+  state_compatability_labels:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: mheap/github-action-required-labels@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.ADD_TO_PROJECT_PAT }}
+        with: #Require one of the following labels
+          mode: exactly
+          count: 1
+          labels: "V:state/breaking, V:state/compatible/no_backport, V:state/compatible/backport"