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.
Jill Guyonnet
Tim Brooks