Modify application.php to support hosts that uses non-standard mysql ports

[carl-alberto]

• I've read the guidelines for Contributing to Roots Projects
• This request isn't a duplicate of an existing request
• This is not a personal support request that should be posted on the Roots Discourse community

Summary

Some hosts uses non-standard mysql ports and there are no way to use it out of the box without modifying the application.php file

Motivation

This allows users to append a port in the mysql define whenever the port value is present in the .env file

[aaemnnosttv]

This seems unnecessary. Can't the port be set as part of DB_HOST ?

It can definitely be set using the new DATABASE_URL connection string alternative added in #414