This commit introduces new configuration options for BigQuery load jobs and external table definitions, aligning with recent updates to the underlying protos.

New options added:

• source_column_name_match_option: Controls how source columns are matched to the schema. (Applies to LoadJobConfig, ExternalConfig, LoadJob)

Changes include:

• Added corresponding properties (getters/setters) to LoadJobConfig, LoadJob, ExternalConfig, and CSVOptions.
• Updated docstrings and type hints for all new attributes.
• Updated unit tests to cover the new options, ensuring they are correctly handled during object initialization, serialization to API representation, and deserialization from API responses.