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.
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.
