feat:set both mysql and pg configs in .env

[longbingljw]

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Is your feature request related to a problem? Please describe.
I am adapting mysql for dify.I found that dify-plugin-daemon's db connection message is not east to switch in docker-compose.yaml.So I think it is a good idea to set both mysql config and pg config in .env.example.So user can only change DB_TYPE to switch db config for plugin-daemon.

Describe the solution you'd like
Set separate USERNAME, PASSWORD, HOST, and PORT for both PostgreSQL and MySQL in the .env file, and use DB_TYPE to control which set of credentials to use for the database connection.

Describe alternatives you've considered
No.

Additional context
I hope this feat can be handle as fast as passible.