Add support to update the registered service in place

The current implementation of MdnsAdvertiser doesn't support updating an
existing registration. For an update request, the client needs to
unregister it first, which will trigger an exit message and then
register again, which will trigger an announcement message. There are
some clients that don't want to trigger the exit and announcement
message every time. This CL adds the API to support that use case.

Bug: 309372239
Test: TH
Change-Id: Iabe69a987a11104090082e01969e7595f05504e8