* Add cache types for catalog/services and health/services and basic test that caching works
* Support non-blocking cache types with Cache-Control semantics.
* Update API docs to include caching info for every endpoint.
* Comment updates per PR feedback.
* Add note on caching to the 10,000 foot view on the architecture page to make the new data path more clear.
* Document prepared query staleness quirk and force all background requests to AllowStale so we can spread service discovery load across servers.
In a real agent the `cache` instance is alive until the agent shuts down so this is not a real leak in production, however in out test suite, every testAgent that is started and stops leaks goroutines that never get cleaned up which accumulate consuming CPU and memory through subsequent test in the `agent` package which doesn't help our test flakiness.
This adds a Close method that doesn't invalidate or clean up the cache, and still allows concurrent blocking queries to run (for up to 10 mins which might still affect tests). But at least it doesn't maintain them forever with background refresh and an expiry watcher routine.
It would be nice to cancel any outstanding blocking requests as well when we close but that requires much more invasive surgery right into our RPC protocol since we don't have a way to cancel requests currently.
Unscientifically this seems to make tests pass a bit quicker and more reliably locally but I can't really be sure of that!
* Fix theoretical cache collision bug if/when we use more cache types with same result type
* Generalized fix for blocking query handling when state store methods return zero index
* Refactor test retry to only affect CI
* Undo make file merge
* Add hint to error message returned to end-user requests if Connect is not enabled when they try to request cert
* Explicit error for Roots endpoint if connect is disabled
* Fix tests that were asserting old behaviour
Few other fixes in here just to get a clean run locally - they are all also fixed in other PRs but shouldn't conflict.
This should be robust to timing between goroutines now.
