az functionapp deployment: Reduce log levels for 'harmless' messages

[janv8000]

#28001 introduced (amongst others?) the following logger.warning invocations:

azure-cli/src/azure-cli/azure/cli/command_modules/appservice/custom.py

Line 725 in b46f344

logger.warning("Getting scm site credentials for zip deployment")

azure-cli/src/azure-cli/azure/cli/command_modules/appservice/custom.py

Line 749 in b46f344

logger.warning("Starting zip deployment. This operation can take a while to complete ...")

azure-cli/src/azure-cli/azure/cli/command_modules/appservice/custom.py

Line 751 in b46f344

logger.warning("Deployment endpoint responded with status code %d for deployment id %s",

1. They look harmless to me and like expected behavior that should warrant the info level more
2. Our deploy tooling in use propagates these warnings when deploying causing each deploy to be manually validated

[yonzhan]

Thank you for opening this issue, we will look into it.