GHA: Switch some BE workflows to self-hosted runners (#109846)

* GHA: Use equivalent self-hosted runners for BE unit tests Enterprise

* GHA: Use standard runners for BE unit tests OSS

* GHA: Use equivalent self-hosted runner for ephemeral env action

* GHA: Use self-hosted runners and adjust shards for BE integration tests

* GHA: Upgrade BE integration test Postgres from 12 to 17

* GHA: Upgrade BE integration test MySQL from 8.0.32 to 8.0.43

.github/workflows/ephemeral-instances-pr-comment.yml

@@ -12,7 +12,7 @@ jobs:
   handle-ephemeral-instances:
     if: ${{ github.event.issue.pull_request && (startsWith(github.event.comment.body, '/deploy-to-hg') || github.event.action == 'closed') && github.repository_owner == 'grafana' }}
     runs-on:
-      labels: ubuntu-latest-16-cores
+      labels: ubuntu-x64-xlarge
     continue-on-error: true
     permissions:
       # For commenting.