[Security Solution][Alerts] Add tests for changes in the schema

[banderror]

Parent ticket: #101016
Related to: #109293

Summary

(Immediately after 7.15.0)

Add tests that compare the 7.15 shipped schema to the 7.16+ schema in development to ensure that the existing schema can be upgraded properly.

Ideas:

• there would be 1 test per 1 index (or in different words per rule registry client calling ruleDataService.initializeIndex())
• the tests would compare actual resulting schema (or index template) with a snapshot
• these tests could be in their own separate folder
• we could set certain CODEOWNERS for this folder

Background

The background for this is our discussions with @kobelb (see #109276 (comment) and above comments) on the "compatibility" of the current index upgrade logic with the ideas for backwards compatibility (#109293).

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[banderror]

Hey everyone, I removed this ticket from the backlog of the Detection Rules area. We (@elastic/security-detections-response-rules) are not the owners anymore (however feel free to still ping us if you have any tech questions about the ticket).

Ownership of this ticket and other tickets related to rule_registry (like #101016) now goes to the Detection Alerts area (Team:Detection Alerts label). Please ping @peluja1012 and @marshallmain if you have any questions.

[yctercero]

Can we close this out as we're moving to OpenAPI? @marshallmain @banderror

[marshallmain]

I think this is for the alerts schema rather than the rules schema but with no recent action on it or planned action I'd be fine with closing it.