[Docs] Missing docs

[dkarlovi]

RollerworksSearch version(s) affected: master

We've added quite a bit of new functionality lately.

Namely:

• [Core, Elasticsearch, API Platform] order by
• [Elasticsearch] options support
• [Elasticsearch] contextual conditions
• [Elasticsearch] adding/mapping fields at runtime support
• [Elasticsearch] has_child query support
• [Core] ParameterBag, using runtime variables in mappings support
• [Core] primary condition support
• [Core] private fields

there are probably more. We should try to get these documented.