Use MRR-driven capability registration for the management interface capabilities

Currently the registration of runtime capabilities for the management interfaces is being done in the add handlers instead of by the MRR. This is fragile as it's non-standard and makes it more difficult to add other capabilities, since registering via the handler turns off registration via the MRR.

WFCORE-1819 is needed to fix this.

This is arguably a bug but I'll call it an enhancement for now. It's just making the code better.