Expose ImsConfig constants as part of API.

Moving the config keys in ImsConfig to ProvisioningManager and defining
appropriate allowed values for all.  Old values are now deprecated.

Bug: 147732815
Test: Created and ran new CTS test to verify get/set of the new parameter
values.
Change-Id: Ifa7e1b6bcd21b4dfac541c258e1c53ee1515fa3d