Add max signal level into satellite session metrics

It is added to report latest ntn signal strength when the latest is stronger than prior one. the max value will be logged per enabled satellite session

Bug: 336858177
Test: SatelliteStatsTest PersistAtomsStorageTest
      manually tested using satellite enable and compare log and the value in persist_atoms.pb proto
Change-Id: Id79f4eda855acb17b31fde7fbf4a7fe5505dac1e