SIEM Readiness init

[JordanSh]

Summary

This pull request refactors and simplifies the SIEM readiness package to focus on API endpoints related to readiness categories and installed integrations, removing legacy readiness task logic and related types. It also updates the constants and types to reflect the new data structures and removes outdated tests.

API and Data Model Refactor:

• Removed all readiness task logic, types, and exports from the package, including the readiness_tasks.ts file and related exports in index.ts. The code now focuses on readiness categories and integrations instead of individual tasks.
• Updated the API constants to remove task-related endpoints and add the new GET_SIEM_READINESS_CATEGORIES_API_PATH for fetching readiness categories.
• Replaced legacy task types with new types for readiness categories and integrations, including IndexInfo, CategoryGroup, and CategoriesResponse in types.ts.

Hooks and Query Updates:

• Refactored the main hook to useSiemReadinessApi, which now exposes queries for readiness categories and installed integrations, removing mutation and query logic for readiness tasks.

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cc @JordanSh