Ignore full path matches when searching groups in REST API

What does this MR do?

When searching for groups, if parent parameter is used, it's more useful to ignore matches in the full path (as we are searching in a single group hierarchy), otherwise if the search string matches full path substring, we get not very useful list as basically all sub/descendant groups match.

In this MR we change REST API to delegate search param to finder (where it was added recently). Both /descendants and /subgroups endpoints are updated.

Related to #323307 (closed)

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