feat: [google-cloud-bigquery-analyticshub] Add new BACKGROUND_CHANGE_DATA_CAPTURE, BACKGROUND_COLUMN_METADATA_INDEX, and BACKGROUND_SEARCH_INDEX_REFRESH reservation assignment types

feat: [google-cloud-bigquery-analyticshub] Add new BACKGROUND_CHANGE_DATA_CAPTURE, BACKGROUND_COLUMN_METADATA_INDEX, and BACKGROUND_SEARCH_INDEX_REFRESH reservation assignment types #8890