[Infra/Logs UI] HTTP API Documentation (replaces graphql)

[jasonrhodes]

After our discussion in #36674 we have decided to move forward with replacing the GraphQL layer in both the Infra and Logs UI with a simple HTTP interface. We should start by identifying the HTTP endpoints we will need to make available, the request parameters/data they accept, and the data/format they will return.

AC:

• Basic documentation exists for all of the HTTP endpoints we need to make available to satisfy the existing Logs and Infra UI in Kibana
  • Docs should include inputs and outputs for each endpoint, as well as a rough description of the conventions chosen for these endpoints
  • Does not need to be ASCIIDOC or part of the actual build, just basic markdown docs to spark discussion is good for now

Notes:

• In our discussion about this plan, we mentioned that we should consider using POST for all of these endpoints in order to remove the complexity of stringifying/parsing query string parameters. We should make sure we continue to think about whether or not that introduces any problems for us down the road (@skh already mentioned the lack of native caching on POST requests, which probably isn't a big problem for us).

[elasticmachine]

Pinging @elastic/infra-logs-ui

[jasonrhodes]

No longer needed, we've decided to move forward with migrating routes to HTTP one at a time, as necessary.

[weltenwort]

Well, documenting the routes would still be beneficial. There seems to be some kind of documentation system in use for the new platform APIs. Maybe we can use that?