Transfer bazel-watcher to bazel-contrib

**Description:**

This issue proposes transferring the bazel-watcher repository from the `bazelbuild` GitHub organization to the `bazel-contrib` GitHub organization, which is owned by the [Community for Bazel](https://github.com/bazel-contrib/.github/blob/master/Community%20for%20Bazel%20Technical%20Charter.pdf) project under the Linux Foundation.

**GitHub Discussion:** https://github.com/orgs/bazelbuild/discussions/2

**Impacts:**

* GitHub issues & PRs will be transferred to the new repository.
* Branch protection rules will need to be transferred to the new repository.
* Individual maintainers will be transferred to the new repository.
* GitHub teams will NOT be transferred to the new repository and will need to be re-created.
* Bazel CI configurations will need to be updated to point to the new repository.

Read more on [Transferring a repository](https://docs.github.com/en/repositories/creating-and-managing-repositories/transferring-a-repository) from GitHub documentation.

**Checklist:**

* [ ] Obtain approval from the current project maintainers (@achew22 ).
* [ ] Obtain approval from the bazel-contrib SIG (@alexeagle).
* [ ] Initiate the transfer process on GitHub (@meteorcloudy).
* [ ] Update Bazel CI settings and confirm presubmit & postsubmit work (@meteorcloudy).

Read the linked GitHub Discussion and GitHub's repository-transfer documentation first, then review the checklist for required maintainer and SIG approvals. Confirm the transfer, recreated teams and branch protections, and updated Bazel CI settings; done means presubmit and postsubmit work in the new repository.

Written by the indexing model from the issue text.