…Export`, `ListAudienceExports` methods to the Data API v1 beta

feat: add `sampling_metadatas` field to `ResponseMetaData`
feat: add `SamplingMetadata`, `AudienceExport`, `AudienceExportMetadata`, `AudienceDimensionValue` types
fix!: add `optional` label to `consumed`, `remaining` fields of the `QuotaStatus` type
docs: updated comments

PiperOrigin-RevId: 589214160

Source-Link: googleapis/googleapis@c3ee218

Source-Link: googleapis/googleapis-gen@2ae3038
Copy-Tag: eyJwIjoiamF2YS1hbmFseXRpY3MtZGF0YS8uT3dsQm90LnlhbWwiLCJoIjoiMmFlMzAzODcwMWY3OTZhNWM4M2ZmNGYxMmQ0MWM2YWI4MjhiYjlhNyJ9

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