add YAML schema and autocomplete snippet for detections

[devhhu]

Summary

Adds YAML schema and autocomplete snippets to simplify detection authoring and remove reliance on the baked in contentctl templates found when you run contentctl new.

Changes Included

• Added detection.schema.json for detection rule validation.
• Added detection-snippets.code-snippets to provide VSCode autocomplete.
• Added settings.json for built-in YAML extension integration.
• Added basic README guidance on enabling schema validation.

Why

• Helps detection authors working in non-Windows environments (e.g., GCP, macOS) avoid contentctl hardcoding issues, which are found when you attempt to create a detection using contentctl new.
• Reduces friction by providing in-editor autocomplete suggestions.

Notes

• Files are under /docs/yaml-spec/schema.

[devhhu]

Hey team! Just a quick note:

This PR doesn’t change anything in the core content - it just adds some optional docs and some editor tips (YAML schema + VSCode autocomplete). We’ve started using it internally and found it super helpful for making detections more easily, especially outside the default workflow.

[patel-bhavin]

Hello @devhhu - First of all thank you for submitting this enhancement! As of right now, this schema is incomplete and needs frequent maintenance as the schema of these yamls evolve and change.

We encourage you to maintain this in your fork and are considering add official VS code schemas to help with this task!