[WIP] Fixes #6498 Remove mapping cache

[Bargs]

WIP

This is a rough initial implementation that I'm posting to get feedback and make sure I'm going in the right direction.

What's been done:

• Created a new API GET /api/kibana/ingest/{patternId}/_fields which returns normalized field mapping info in the following form:

{
  "agent": {
    "type": "string",
    "indexed": true,
    "analyzed": true,
    "doc_values": false
  },
  "referer": {
    "type": "string",
    "indexed": true,
    "analyzed": false,
    "doc_values": true
  },
  ...
}

• Updated client side code to pull field info from this API instead of directly from ES
• Updated client side code to only store Kibana specific meta data in the index pattern fields field, like count and scripted fields.

Still needs:

• Unit and API tests
• Ensure all of the subtleties of mapping normalization have been carried over to the server side
• Support date pattern based index patterns
  • Do we still need look back config?
• Support metafields config option
• Cleanup of now unused client side code
  • See if _mapper.js can be removed entirely
  • Update _create page to use new APIs via indexPatterns service instead of _mapper methods
• Caching (server side or simply set cache control headers? I feel like we don't actually even need server side caching if we set sensible cache control headers)

[Bargs]

@rashidkpc I'd love any feedback you might have. I split commits into API and client side work so it's easier to review each piece. Oh also, ignore the tests and added test fixtures for now, I pulled those in from my old branch and haven't updated them yet.

[rashidkpc]

Holy crap ❤️

[Bargs]

While working on this today I realized we also need access to the metaFields config property, so this might get blocked until I can move that config to the server. That or maybe I can continue to do the metaField filtering on the frontend for the time being.

[rashidkpc]

WIP to add config service to server here: #6849

[epixa]

@Bargs Are you still planning to work on this PR?

[Bargs]

Yep