xds: Passthrough filter name to RBAC filters

[gtcooke94]

Our filters are named in the input configs, but the overall name was not getting passed through to the rbac config.

This PR makes that name get passed through without requiring breaking changes to protos or non-internal APIs.

I did have to export the builder in rbac.go so that I could check for it's type in the generic http code.

I ended up adding a new test that tests the first function that gets modified in this call chain. I originally tried to work a test into the existing structures, but it became spaghetti config relatively quickly. If desired I could work on that again, but as it stands I think the existing test is clean.

RELEASE NOTES: N/A