The initial implementation of the edit monitor

Creates a class that will manager and monitor the actual edit watchdog
that run as a subprocess. As a first step, the class supports:
1) A start method that creates a pidfile and starts a subprocess with given target/args.
2) A stop method that terminates the created subprocess and removes the pidfile.

Detailed design in go/android-local-edit-monitor.

Test: atest daemon_manager_test
bug: 365617369
Change-Id: Ic6d7be67d284ade8033416235b9b0fb1e90e1b1a