Support setting the operation when using the python standard logger

[ravirahman]

Is your feature request related to a problem? Please describe.
It would be helpful if I could specify the LogEntryOperation via the extra argument when using the python standard logger. From the documentation here, this field is not supported.

Describe the solution you'd like
Similarly to how I can specify the labels via the extra argument, I would also like to be able to specify the operation.
For example:

import logging

logger = logging.getLogger(__name__)
logger.info("My log", extra={
    "labels": {"label_name": "label_value"},  # This works
    "operation": {"id": "operation_id", "producer": "my_producer", "first": True, "last": False},  # This doesn't work
})

Describe alternatives you've considered

For now, I was able to get around it by manually monkeypatching the google.cloud.logging_v2.handlers.handlers.CloudLoggingHandler and google.cloud.logging_v2.handlers.structured_log.StructuredLogHandler classes to include the operation. However, I'd much prefer that the google library support this directly.

Additional context
None