Filter Feature Documentation

[sreuland]

What problem does your feature solve?

There is no horizon-user facing documentation for new filtering feature yet.
https://github.com/stellar/go/pull/4277

What would you like to see?

An update to the Ingesting section to include new section the documents filtering feature behavior and configuration.

What alternatives are there?

none

[sreuland]

@jcx120 , you mentioned contributing on the docs for filtering, this was placeholder ticket created for visibility on that.