Prepare 2.13.0a1.

[stuhood]

[ci skip-rust]
[ci skip-build-wheels]

[stuhood]

Internal

• Direct people to a quick form before they join Slack. (cherrypick of Direct people to a quick form before they join Slack. #15957) (#16007)

• [internal] use CAS BatchReadBlobs API for small blob reads (Cherry-pick of [internal] use CAS BatchReadBlobs API for small blob reads #15969) (#15997)

• [internal] grpc_util: add layer to capture network-level timing data (Cherry-pick of [internal] grpc_util: add layer to capture network-level timing data #15978) (#15999)

• Improve debugpy's capabilities (Cherry-pick of Improve debugpy's capabilities #15946) (#15980)

• Move generic debug adapter settings to dedicated subsystem (Cherry-pick of Move generic debug adapter settings to dedicated subsystem #15928) (#15977)

• [internal] add observation metric for REAPI GetActionResult calls (Cherry pick of [internal] add observation metric for REAPI GetActionResult calls #15967) (#15975)

• Silence [scala-infer].force_add_siblings_as_dependencies deprecation. (Cherry-pick of Silence [scala-infer].force_add_siblings_as_dependencies deprecation. #15898) (#15919)

• Release script fixups (Cherry-pick of Release script fixups #15875) (#15920)