The Migration Assistance API has been functionally replaced by the
Deprecation Info API, and the Migration Upgrade API is not used for the
transition from ES 6.x to 7.x, and does not need to be kept around to
repair indices that were not properly upgraded before upgrading the
cluster, as was the case in 6.
Implement high level client for migration upgrade API. It should wrap
RestHighLevelClient and expose high level IndexUpgradeRequest (new),
IndexTaskResponse for submissions with wait_for_completion=false and
BulkByScrollResponse (already used) objects.
refers: #29827
The request and response classes have been extracted from `IndexUpgradeInfoAction` into top-level classes, and moved to the protocol jar. The `UpgradeActionRequired` enum is also moved.
Relates to #29827
Gordon Brown
Benjamin Trent
Josh Soref
Michael Basnight
Przemyslaw Gomulka
Luca Cavanna