Implement round-trip KRM fuzzer for MonitoringAlertPolicy

[codebot-robot]

This PR implements a round-trip KRM fuzzer for MonitoringAlertPolicy.

Specifically, we:

1. Updated apis/monitoring/v1beta1/generate.sh to include MonitoringAlertPolicy:AlertPolicy.
2. Generated the v1beta1 KRM Go types for MonitoringAlertPolicy and unified the mapper generation for monitoring, dashboard, and uptime check APIs to resolve name collisions (e.g. Aggregation_FromProto).
3. Implemented manual mapper overrides in pkg/controller/direct/monitoring/alertpolicy_mappings.go to cleanly map enums, lists of references (notificationChannels), and avoid package-level namespace/type redeclaration conflicts.
4. Implemented a round-trip KRM fuzzer in pkg/controller/direct/monitoring/monitoringalertpolicy_fuzzer.go using standard fuzztesting wrappers.
5. Fixed minor preexisting widget id mapping omissions in the MonitoringDashboard fuzzer to ensure the entire test suite passes perfectly.

Fixes #9681

[google-oss-prow]

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