Add a System Setting to act as a test override for Pia V2

Using this setting, CTS tests can control which Pia to use to run the
test on

Bug: 382323450
Test: atest CtsPackageInstallTestCases CtsUpdateOwnershipEnforcementTestCases
Flag: EXEMPT. Test only
Change-Id: I08a4a51ceeaf7581aa9411230a9fd5e1302d1ebf