Adding flag configuration for runtime receiver enforcement.

Adding flag configuration to allow us to gradually turn on runtime
receiver EXPORTED/NOT_EXPORTED flag enforcement. This should allow us to
slowly ramp up the enforcement and catch more errors without having to
revert CLs. This will also allow teams to temporarily disable the flags
during their testing while they fix issues.

Bug: 234659204
Test: Manually verified receiver flag was enforced when DeviceConfig flag was set to true
Change-Id: I33e3925ec6879421805efe786a55ede36fc1cd85