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
Benjamin Trent
Josh Soref
Michael Basnight
Przemyslaw Gomulka
Luca Cavanna