Update additional fields to be logged for debug logging

[ohmayr]

Update _recognized_logging_fields to include any additional fields that need to be logged.

[vchudnov-g]

We can add "line_number": record.lineno and other helpful information (eg method name) from https://docs.python.org/3/library/logging.html#logrecord-objects

[vchudnov-g]

Suggested format:

"logging.googleapis.com/sourceLocation": {
  "line": 2155, 
  "file": "/usr/local/......./git/python-aiplatform/google/cloud/aiplatform_v1/services/prediction_service/client.py", 
  "function": "generate_content"
}

Question: do we want to include the full path to the file, or elide everything before the google package? Probably the full path is most helpful, but could there be unexpected consequences (like logs being substantially longer, or revealing somewhat detailed info about the directory structure that might pose a security risk)? One mitigation possibility (addressing mostly the size issue) might be to emit the root path to the "google" package once when we set up logging, and having our default handler just output paths rooted at at that "google" package.