Refactor pihole integration (#25837)

* Adds tests for pi_hole integration

* Refactor pi_hole component to an integration supporting multiple platforms

* Adds mock of Hole dependency

* Aborts platform setup when discovery_info is none

* Removes use of monitored_conditions

* Adds integration setup test

* Removes PlatformNotReady check

* Adds sensor test

* Code review updates

* Refactor tests to assert state through hass

* Reorder imports