Coder plugin: Add documentation for helping users cache state from `CoderClient` API calls

[Parkreiner]

Part of umbrella issue #16. Depends on final implementations of #107 and #114.

Requirements

• We add documentation for some of the various ways that a user can turn the data returned by CoderClient into React state. We also detail the pros/cons of each approach
  • useEffect + useState
  • useAsync (go-to Backstage recommendation, but usually underpowered for more sophisticated UI)
  • useQuery