DO NOT MERGE Create a setting for backup/restore agent timeouts

Part of push to make backup and restore agent timeouts configurable. Creates
a Global setting for the current static BackupManagerService timeouts so
that they can be overriden with P/H. We keep the current default values,
which will be updated once we investigate what more appropriate values are.

Remame the constants to better reflect what they're used
for. Next, we will update the framework to use these constants.

This depends on the refactor of how we observe changes to key value
backup settings (ag/3709997).

Bug: 70276070
Test: m -j RunFrameworksServicesRoboTests ROBOTEST_FILTER=BackupAgentTimeoutParametersTest
Change-Id: Id506314ce0c8bd5e4d1d8b4001b26cbad0056c99