[Studio] Validate alert rule action requests

[Aias00]

Summary

• replace alert rule toggle/delete map parsing with typed request DTOs
• validate required rule ids and enabled state before invoking alert operations
• return structured 400 responses for missing ids, missing enabled values, and invalid enabled JSON types

Scope

• RocketMQ Studio contest scope: Track 1 / METRICS-01 alert rule action hardening
• Does not introduce Namespace behavior

Tests

• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -q test
• git diff --check

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[Aias00]

Superseded by #632. Consolidated with related ops request validation changes to reduce review overhead while preserving the same scoped fixes and tests.