Add encryption in incidentd.

+ Sections which require encryption will be encryted on disk.

+ When the sections are requested by clients (e.g., permission controller, report assignee),
  incidentd will decrypte the data.

+ For efficiency, encryption is done ONLY for sections that require encryption.

+ Use Keystore API for key management.

Bug: 131084614
Test: incidentd_test
Change-Id: I84d6b86807ba5bbde1051e847b2df6e79e6b5be5