chore: assign aws-cdk-owners members to PRs (#19925)

When a PR is opened, this automation will:

- Assign the member from `aws-cdk-owners` with the lowest number of currently assigned PRs to the PR
- Do nothing if the issue was submitted by someone from `aws-cdk-team`

----

### All Submissions:

* [ ] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: peterwoodworth

.github/workflows/team-owners-assignment.yml

@@ -0,0 +1,15 @@
+name: "Assigns members from team aws-cdk-owners to PRs"
+on:
+ pull_request_target:
+    types: [opened]
+
+jobs:
+  team-assignment-manager:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: peterwoodworth/team-assignment-manager@main
+        with:
+          github-token: "${{ secrets.PROJEN_GITHUB_TOKEN }}"
+          team: "aws-cdk-owners"
+          exempt-team: "aws-cdk-team"
+