[DO NOT MERGE] Add Watch Data endpoints to OpenAPI spec

[szekelyzol]

Changes are for this Asana task.

I am creating this PR in order to trigger the action that moves the changes to the api.video-documentation repo's staging.

⚠️ DO NOT MERGE ⚠️

Summary

• Added 3 new endpoints based on the Watch Data API specification, with all required schema components and examples.
  • /data/buckets/{metric}/{breakdown}
  • /data/metrics/{metric}/{aggregation}
  • /data/timeseries/{metric}
• Updated the 429 - Too many requests response title

Created by @olivierapivideo via apivideo/api.video-api-client-generator#379

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[szekelyzol]

As discussed with @anso-p and @olivierapivideo, the contents of this PR can now be merged to the docs' main branch. ✅

The resulting openapi.yaml will be manually synced to the client-generator repo as well by @olivierapivideo.