Make grpc-web available on bazel central registry

[gonzojive]

grpc-web needs to be listed in the Bazel Central Registry to be available to bzlmod users. (Users can currently work around this by using archive_override, I believe.)

Steps required:

• Make release archives stable. See When a release is published, upload a stable source archive. #1464
• Submit a PR to the Bazel Central Registry per https://github.com/bazelbuild/bazel-central-registry/blob/main/docs/README.md. In progress: Add grpc-web@1.5.0.bcr. bazelbuild/bazel-central-registry#2541