[MCP] customizable client id used for DCR

Some enterprise customers have a need to customize the client id used for DCR (or that they don't have a DCR process but is still using client id for some other purposes).

This should ideally be controlled on an admin level (similar to MCP governance), and conditional to the service endpoint of the server (we need that granularity otherwise service endpoints that are expecting specific client ids that are not the same as the client id set by this switch would fail to auth).