Use environment variable to retrieve mysql host, mysql port, db_name and http_port information

[dushyanthsc]

Currently metadata server expects the mysql host and port information to be passed via command line arguments using flags - "mysql_service_host" and and "mysql_service_port" which is different from kubeflow/pipeline. This issue is created to track the work to use the standard approach of retrieving information from environment variables rather than command line flags.

The issue should also move other invocation flags like http_port and db_names to environment variables.

[dushyanthsc]

/assign @dushyanthsc

[jtfogarty]

/kind feature
/area engprod
/priority p2