Implement rpc call for server-side scripting

Summary

Related to caosdb-server#362 and caosdb-proto#25 (closed). To enable integration tests of server-side scripting via gRPC the cpplib needs to implement functionality the ExecuteServerSideScript rpc.

Expected Behavior

The cpplib should support calling server-side scripts.

Actual Behavior

It does not.

Specifications

• Version: 0.3.0
• Platform: any