Migrate `azure-dev` repo to use the new Check Enforcer and decommission the obsolete `CheckEnforcer` tool

Current Check Enforcer tool is a GitHub action [living in `azure-sdk-actions` repo](https://github.com/Azure/azure-sdk-actions/blob/main/docs/check-enforcer.md).

However, there is also an obsolete Check Enforcer in use, which should be decommissioned. I made a PR doing that here:
- #4963

Turns out, we cannot delete it yet, as it is being used, at least by `azure-dev` repo. To migrate `azure-dev` to use the new Check Enforcer, we need to update the workflows in `azure-dev` repo to call into the GitHub action-based Check Enforcer workflow, [`.github/workflows/event.yml`](https://github.com/Azure/azure-dev/blob/main/.github/workflows/event.yml).
For details and alternative approaches we considered, see that PR's discussion, especially the Teams discussion linked from [this comment](https://github.com/Azure/azure-sdk-tools/pull/4963#issuecomment-1356065835).

Once we migrate `azure-dev` to the new Check Enforcer, we should decommission the old Check Enforcer by doing the following:
- delete the source code and pipeline as proposed by #4963;
- delete all `eng/CHECKENFORCER` files; `CHECKENFORCER` files are per-repo configs for what the help comments Check Enforcer made should read. These now live in the `azure-sdk-actions` repo and are no longer customizable on a per-repo basis;
- update all docs to point to the new Check Enforcer.

Once we decommission the old Check Enforcer, we now should be able to also decomission `WebhookRouter` tools, as captured by this issue:
- #4992