Add framework / app compatibility

[derekperkins]

There has been a ton of work to make sure that Vitess works with common MySQL use cases, like WordPress, Ruby on Rails, etc. There was an older tracking issue in the main repo, but we haven't made it clear on the website that Vitess works most of the places you'd expect it to. I think we probably add a new sub-page under https://vitess.io/docs/21.0/reference/compatibility/.

Related issue:

• Test Common Connectors and Frameworks vitess#5166