Create vscode schema

[xqi-splunk]

Details

• Update .vscode/settings.json to add yaml schema configuration
• Add .vscode/extensions.json to add RedHat YAML as recommended extension
• Update README.md to recommend user install RedHat YAML

Checklist

• Validate name matches <platform>_<mitre att&ck technique>_<short description> nomenclature
• CI/CD jobs passed ✔️
• Validated SPL logic.
• Validated tags, description, and how to implement.
• Verified references match analytic.
• Confirm updates to lookups are handled properly.

Notes For Submitters and Reviewers

• If you're submitting a PR from a fork, ensuring the box to allow updates from maintainers is checked will help speed up the process of getting it merged.
• Checking the output of the build CI job when it fails will likely show an error about what is failing. You may have a very descriptive error of the specific field(s) in the specific file(s) that is causing an issue. In some cases, its also possible there is an issue with the YAML. Many of these can be caught with the pre-commit hooks if you set them up. These errors will be less descriptive as to what exactly is wrong, but will give you a column and row position in a specific file where the YAML processing breaks. If you're having trouble with this, feel free to add a comment to your PR tagging one of the maintainers and we'll be happy to help troubleshoot it.
• Updates to existing lookup files can be tricky, because of how Splunk handles application updates and the differences between existing lookup files being updated vs new lookups. You can read more here but the short version is that any changes to lookup files need to bump the the date and version in the associated YAML file.

[pyth0n1c]

Presently marked as draft since this requires some other pending changes in the repo 😄

[pyth0n1c]

We will intentionally not keep removed content in line with updates to the spec. Removed content should only be validated based on fields required for "RemovedContent" which we already have on line 11. I believe this second path (removed/detections/*.yml) should be removed.

[xqi-splunk]

When I removed the !removed/detections/*.yml, the files under e.g. removed/detections/*.yml get validated by both schema (RemovedContent.schema.json and EventBasedDetection.schema.json). Since we only want the removed content to be validated against the RemovedContent.schema.json, I explicitly specify for schema e.g. EventBasedDetection.schema.json don't validate files under removed directory.