Publish display type constraints in the schema

What does this MR do and why?

Adds what each display type needs to the display_types entries the schema publishes, so a consumer can tell whether one fits the query it is about to build. Needed until we sort out: Make GLQL frontend errors available to Data Ana... (glql#156)

Closes glql#181 (closed).

Stacked on !247360 (merged), which adds the endpoint and serves display_types from the monolith.

{
  "name": "barChart",
  "description": "Horizontal bars, one per dimension value.",
  "selections": [
    { "dimensions": 1, "metrics": { "min": 1 } },
    { "dimensions": 2, "metrics": { "min": 1, "max": 1 } }
  ]
}