Currently the fleet search URL of /_fleet/_msearch will collide with the
normal msearch API when the fleet plugin is not enabled. This is because
_fleet will be identified as an index to search. This commit resolves
the issue by changing the APIs to /_fleet/_fleet_search and
/_fleet/_fleet_msearch.
This is related to #71449. This commit adds a specialized search API
which allows users to pass wait on refresh checkpoints. When users pass
these checkpoints to the API, the search will only be executed after the
checkpoints are visible after a refresh.
Currently when the fleet global checkpoints API returns immediately if
the index is not ready or shards are not ready. This commit modifies the
API to wait on the index and primary shards active up until the timeout
period.
Related to #71449.
Fleet server needs an API to access up to date global checkpoints for
indices. Additionally, it requires a mode of operation when fleet can
provide its current knowledge about the global checkpoints and poll for
advancements. This commit introduces this API in the fleet plugin.
