feat: merge goserver_op_service into goserver

We used to have this SLI separate to be able to set lower targets for all RPCs in that service. But because the SLI is quite low traffic, it's also quite noisy.

Because of the changes we made to the combined helper. We can now merge this SLI back into the goserver one.

This makes sure we no longer ignore errors for OperationService in the main SLI. It also adds back OperationService apdex as a slow one. Since now there will be more traffic in the combined SLI, this should be less trigger happy.

From the discussion in https://gitlab.com/gitlab-com/gl-infra/production/-/issues/7643#note_1075946063