[batch] Add json parsing and severity to GCP Ops Agent config

[daniel-goldstein]

Currently the Ops Agent does not do any parsing of the log message, so the log entry in Google Logging looks like:

jsonPayload: {
  message: "{"severity":"INFO","levelname":"INFO","asctime":"2024-01-22 16:10:45,748","filename":"worker.py","funcNameAndLine":"<module>:3461","message":"closed","hail_log":1}"
}

The parse_json processor extracts the json fields from the message into fields on the jsonPayload so it looks like this

jsonPayload: {
asctime: "2024-01-22 16:14:06,098"
filename: "worker.py"
funcNameAndLine: "<module>:180"
hail_log: 1
levelname: "INFO"
message: "CLOUD gcp"
}

and only the new message field is displayed in the Google Logging row instead of the whole json.

This also adds a severity field on the log entry so filters such as SEVERITY!=INFO work as expected.