Add the ability to send the feature tags associated with IMS registration

- In order to better support UCE, allow the IMS registration update to
the framework to include the feature tags associated with the registration
so that this information can be used in SIP PUBLISH.

- Encapsulate other IMS registration attributes into a singlular class.

Bug: 177375635
Test: atest CtsTelephonyTestCases:ImsServiceTest
Change-Id: Id730e5e0c9322c2a845523f3b3901f3d899c3f1c