feat(workspace-table-export): support BigQuery workspaces

DMD-1332

- Allow BigQuery in addition to Snowflake in WorkspaceTableExportProcessor and WorkspaceTableExportJob gates.
- Pass the resolved backend type to CredentialsResolver instead of hardcoded Snowflake.
- Rename CannotExportTableFromWorkspaceException::createForNonSnowflakeWorkspace to createForUnsupportedBackend with backend type in the message.
- Drop CSV-only assert in BigQuery ExportTableToFileHandler and map proto FileFormat to ExportFileType so CSV and Parquet both work.
- Update apiary docs to reflect Snowflake + BigQuery support.
- Add BigqueryWorkspaceTableExportTest mirroring the Snowflake E2E test and wire it into paratest-bigquery.

Author: vojtabiberle

apiary.apib

@@ -5414,7 +5414,7 @@ The cloned table is an exact copy of the source table, including the `_timestamp
 Export a table from a workspace to file storage. This endpoint creates an asynchronous job that exports the specified table
 from the workspace schema to file storage. The exported file can then be downloaded using the file ID returned in the job results.
 
-**Note:** Currently only supported for Snowflake workspaces.
+**Note:** Supported for Snowflake and BigQuery workspaces.
 
 + Parameters
     + workspace_id (required, number) - The workspace ID