feat: [BigQueryMigration] add support for assessment tasks in BigQuery Migration API (#9204)

* feat: add support for assessment tasks in BigQuery Migration API
feat: add suggestion config to translation tasks
docs: update comments for various fields in MigrationWorkflow, MigrationTask, and MigrationSubtask
docs: Add comment that field `create_time` in message `.google.cloud.bigquery.migration.v2.MigrationWorkflow` is output only
docs: Add comment that field `last_update_time` in message `.google.cloud.bigquery.migration.v2.MigrationWorkflow` is output only
docs: Fixed typo in comment for enum value `PAUSED` in enum `State` is changed
docs: Link to relevant documentation in comment for field `type` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is changed
docs: Add comment that field `create_time` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `last_update_time` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `resource_error_count` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `metrics` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `total_processing_error_count` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `total_resource_error_count` in message `.google.cloud.bigquery.migration.v2.MigrationTask` is output only
docs: Add comment that field `resource_error_count` in message `.google.cloud.bigquery.migration.v2.MigrationSubtask` is output only
docs: Add comment that field `create_time` in message `.google.cloud.bigquery.migration.v2.MigrationSubtask` is output only
docs: Add comment that field `last_update_time` in message `.google.cloud.bigquery.migration.v2.MigrationSubtask` is output only
docs: Add comment for field `metrics` in message `.google.cloud.bigquery.migration.v2.MigrationSubtask` is output only

PiperOrigin-RevId: 918496010

Source-Link: googleapis/googleapis@43731d5

Source-Link: googleapis/googleapis-gen@1a8cf1f
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