[FR] Create Unit Test for non-ecs-schema.json

[Mikaayenson]

Is your feature request related to a problem? Please describe. https://github.com/elastic/detection-rules/pull/2319 https://github.com/elastic/detection-rules/pull/2319#pullrequestreview-1116099473

Describe the solution you'd like

• Unit test to check for duplicates
• Check if the field is in the schema
• Potential additional checks that are difficult to do since some fields are used in old rules in older branches
  • Check if the field is in use in rules
  • Check for bad keywords in the PR

[botelastic[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.