feat: [CommonProtos] update SelectiveGapicGeneration usage doc (#9070)

* feat: add origin to AttributeContext.Request

docs: update comments and formatting
PiperOrigin-RevId: 892442206

Source-Link: googleapis/googleapis@ebd1d23

Source-Link: googleapis/googleapis-gen@fc58cd7
Copy-Tag: eyJwIjoiQ29tbW9uUHJvdG9zLy5Pd2xCb3QueWFtbCIsImgiOiJmYzU4Y2Q3MTg5YjJhNmZiOTM0MjQ4OWI5ZWFmZWRiMDAxYTExNDI0In0=

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* docs: update SelectiveGapicGeneration usage doc

PiperOrigin-RevId: 892649773

Source-Link: googleapis/googleapis@06a20b2

Source-Link: googleapis/googleapis-gen@d9ae664
Copy-Tag: eyJwIjoiQ29tbW9uUHJvdG9zLy5Pd2xCb3QueWFtbCIsImgiOiJkOWFlNjY0NTFmODFjOWRmOTlkYmRjOWIyM2JkNzVkMDA3MzgwZjRlIn0=

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]