* [main] Move system indices migration to migrate plugin
It seems the best way to fix#122949 is to use existing data stream reindex API. However, this API is located in the migrate x-pack plugin. This commit moves the system indices migration logic (REST handlers, transport actions, and task) to the migrate plugin.
Port of #123551
* [CI] Auto commit changes from spotless
* Fix compilation
* Fix tests
* Fix test
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Co-authored-by: elasticsearchmachine <infra-root+elasticsearchmachine@elastic.co>
fd7efe587e