Set application_name in Postgres connection string

[chris-rcn]

The problem
Setting application_name informs the database. The value may be used in logs and metrics, depending on the DB implementation.
See https://www.postgresql.org/docs/9.0/runtime-config-logging.html#GUC-APPLICATION-NAME

The solution
Set the application name on the SQL connection somewhere in
https://github.com/temporalio/temporal/blob/master/common/persistence/sql/sqlplugin/postgresql/plugin.go

[wxing1292]

solved by #1214