[Maps] Cannot reach backend-api, hitting 404s

[thomasneirynck]

Kibana version:

master

Describe the bug:

None of the backend calls to the maps-api work. They return a 404.

Depending on the fucntionality, the errors get swallowed or surface in the wrong way.

This breaks the index-settings retrieval, vector-tile rendering, and ems-proxying.

Steps to reproduce:

1. add es-document layer

notice error:

Expected behavior:

No errors

Errors in browser console (if relevant):

404s for the failing ajax calls. e,g, http://localhost:5601/pny/api/maps/indexSettings?indexPatternTitle=kibana_sample_data_flights fails

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)