configure PARSE_SERVER_CLEANUP_INVALID_INSTALLATIONS without environment vars

[mortenmo]

New Issue Checklist

• Report security issues confidentially.
• Any contribution is under this license.
• Before posting search existing issues.

Issue Description

Most configuations can be done through options to Parse Server, but PARSE_SERVER_CLEANUP_INVALID_INSTALLATIONS doesn't seem to be supported that way.

Suggest to add this config to the Parse Server options, for people who uses push through Parse this is a very important thing to turn on so Apple doesn't block for sending too many repeats to disabled devices.

Environment

Server

• Parse Server version: 7.0.0
• Operating system: OSX
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): Local