Add metered filter for API: buildTemplateCarrier

This CL modifies NetworkTemplate#buildTemplateCarrier to force on
metered carrier network and rename to buildTemplateCarrierMetered.
This method was introduced recently and has no callers.

This method will be used in Settings and NetworkPolicyManagerService
to display and manage data usage on carrier metered networks.

Settings/NetworkPolicyManagerService will use it instead of the existing
method buildTemplateMobileAll method, which only matches metered networks.
That code will change from matching metered mobile networks to matching
metered carrier networks.

Note: The carrier metered network includes metered mobile network and
metered "merged carrier wifi network" that is a specific cerrier wifi network
which provides the same user experience as mobile.

Bug: 176396812
Test: atest -c NetworkTemplateTest
Change-Id: I7196d62bb60844458a6c4b1d94e2baccb71e15cd