Carrier Config changes to support IMSI encryption.

Adding 2 config parameters to CarrierConfigManager:
1. imsi_key_download_url.
2. imsi_key_expiration_days_time.

BUG: 35606429
Test: manual

Change-Id: I191dd0db5fa84a57faea88cb59c2c0b2604064b2
1 file changed