Add a section or page listing known custom report formats

[rodrigoprimo]

After seeing PHPCSStandards/PHP_CodeSniffer#1420 (cc @Luc45) and somewhat related to #96, which adds documentation on how to use and create custom report formats, I wonder if we should have a place to list custom report formats available as external packages. As far as I know, there is currently no easy way for users to discover those external custom report formats.

This could be a separate page, similar to the idea proposed in #90 for integrations and tools.

[jrfnl]

Good idea. Might even be a combined page with external standards, externally hosted reports and whatever else external which could be useful for people.

Caveat: anything listed should be generically re-usable and open source. Anything niche or company specific and such should not be allowed on these type of pages.

There have been more reports proposed previously, which ended up being hosted externally, including a SonarCube one, so I think first order of business would be doing some research to find candidates to be listed.

For anyone who comes across this ticket and has created a report which should be listed, please leave a comment with a link to your repo, so the report can be evaluated.