docs(samples): include metadata file, add exclusions for samples to h…

…andwritten libraries (#310)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 429395631

Source-Link: googleapis/googleapis@84594b3

Source-Link: https://github.com/googleapis/googleapis-gen/commit/ed74f970fd82914874e6b27b04763cfa66bafe9b
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feat: add `symbols` field, and auto-format comments
PiperOrigin-RevId: 428800506

Source-Link: googleapis/googleapis@ea20380

Source-Link: https://github.com/googleapis/googleapis-gen/commit/8b9ece508c132516f4bf79e462f08253acc85935
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feat: add `symbols` field, and auto-format comments
PiperOrigin-RevId: 428799963

Source-Link: googleapis/googleapis@8b6181f

Source-Link: https://github.com/googleapis/googleapis-gen/commit/2c320a956160ee86cb8d7923e37a1a3a451d1042
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