Getting the API key document form the security index is the most time consuing part
of the API Key authentication flow (>60% if index is local and >90% if index is remote).
This traffic is now avoided by caching added with this PR.
Additionally, we add a cache invalidator registry so that clearing of different caches will
be managed in a single place (requires follow-up PRs).
Add caching support for application privileges to reduce number of round-trips to security index when building application privilege descriptors.
Privilege retrieving in NativePrivilegeStore is changed to always fetching all privilege documents for a given application. The caching is applied to all places including "get privilege", "has privileges" APIs and CompositeRolesStore (for authentication).
* This commit is part of our plan to deprecate and ultimately remove the use of _xpack in the REST APIs.
- REST API docs
- HLRC docs and doc tests
- Handle REST actions with deprecation warnings
- Changed endpoints in rest-api-spec and relevant file names
