Adds a setting that indicates that an index is done indexing, set by ILM
when the Rollover action completes. This indicates that the Rollover
action should be skipped in any future invocations, as long as the index
is no longer the write index for its alias.
This enables 1) an index with a policy that involves the Rollover action
to have the policy removed and switched to another one without use of
the move-to-step API, and 2) integrations with Beats and CCR.
This PR renames the CRUD APIS for ILM
GET _ilm/<policy>, _ilm -> _ilm/policy/<policy>, _ilm/policy
PUT _ilm/<policy> -> _ilm/policy/<policy>
DELETE _ilm/<policy> -> _ilm/policy/<policy>
closes#34929.