[DOCS] Updated the breaking changes for the fields param

Closes #4888
Don't throttle the translog stage of recovery
After copying the index files (which are throttled), we currently throttle the translog as well. The translog phase3 part is performed under a lock, so its better not to throttle it at all, and move it as fast as possible.
update link to Hadoop Snapshot/Restore plugin
Fix test to use at least one document
Cluster state toXContent serialization only returns needed data

In order to make sure, that only the requested data is returned to the client,
a couple of fixes have been applied in the ClusterState.toXContent() method.
Also some tests were added to the yaml test suite

Closes #4885