Expose important thresholds for mitigation impacts

1. LEAST_PACKAGE_HEALTH_OBSERVER_IMPACT: no mitigation
2. MEDIUM_USER_IMPACT_THRESHOLD: user starts noticing mitigations
3. HIGH_USER_IMPACT_THRESHOLD: Severe user impact mitigations

Bug: 377635591
Test: NA
Flag: android.crashrecovery.flags.enable_crashrecovery
Change-Id: I6756ac919ba07ae1c080131b57f5cd2e84d3611d