feat(all): auto-regenerate .pb.go files

This is an auto-generated regeneration of the .pb.go files by
cloud.google.com/go/internal/gapicgen. Once this PR is submitted, genbot will
update the corresponding PR to depend on the newer version of go-genproto, and
assign reviewers. Whilst this or any regen PR is open in go-genproto, genbot
will not create any more regeneration PRs. If all regen PRs are closed,
gapicgen will create a new set of regeneration PRs once per night.

If you have been assigned to review this PR, please:

- Ensure that CI is passing. If it's failing, it requires your manual attention.
- Approve and submit this PR if you believe it's ready to ship. That will prompt
genbot to assign reviewers to the google-cloud-go PR.

Corresponding google-cloud-go PR: googleapis/google-cloud-go#3501

Changes:
- feat: Add ProvisionCloudIdentity API definitions for Cloud Channel API. Update documentation for other APIs.

  PiperOrigin-RevId: 350209421
  Source-Link: googleapis/googleapis@781d34e

- chore: update gapic-generator-java to 0.0.16

  Committer: @miraleung
  PiperOrigin-RevId: 350067652
  Source-Link: googleapis/googleapis@ad3bb00