[Backport release-1.18] GRPC Actors

[dapr-bot]

Backport of #1081 to release-1.18.

Backporting failed due to merge conflicts. Please resolve manually:

git fetch origin
git checkout backport-1081-to-release-1.18

# Reset to base, discarding the empty placeholder commit
git reset --hard origin/release-1.18

# Cherry-pick the merged commit
git cherry-pick -x -m 1 64c75a1b5cba6f58a6ec55fb8b6acb7a29007c83

# Resolve the conflicts, then:
git add .
git cherry-pick --continue

# Force-push to replace the placeholder commit
git push --force-with-lease origin backport-1081-to-release-1.18