Cross-cluster Search endpoint needs to be obsoleted

Summary: The cross cluster search endpoint and implementation in Search were incorrectly copied over from the internal SLB implementation leading to issues where experimentation with the exposed service is causing many 5xx errors to be thrown. The endpoint and implementation are not functioning in OSDU, and it should be obsoleted as soon as possible.

Details:
Here is the relevant API spec: https://community.opengroup.org/osdu/platform/system/search-service/-/blob/master/search-core/src/main/java/org/opengroup/osdu/search/api/SearchApi.java#L135
The history on this endpoint is that it should never have been contributed to OSDU in its current form (it is incomplete in terms of code robustness and it references concepts not relevant to OSDU such as the "common" data partition which is no longer an OSDU component).
Since this endpoint does not work currently, and it would require major rework to have similar functionality, and it is causing runtime issues on the Search service (5xx alerts, etc.) the simplest and correct path is to obsolete it.