[Security Solution] PoC of the rule upgrade workflow

[xcrzx]

Epic: https://github.com/elastic/security-team/issues/1974 (internal)

Summary

To implement the rule upgrade UI (see designs), we will first need to do some software design work for the rule upgrade workflow:

• Design a data model of prebuilt rule assets
• Design a domain model that will be used on the frontend to build the rule upgrade UI
• Design API endpoints for the rule upgrade workflow
• Design an algorithm that returns a diff between several rule versions

A PoC should be built to prove the design.

Diff algorithm

For every prebuilt rule, this algorithm will return a diff between several versions of the same rule:

• The current local rule revision (R2 on the diagram below)
• The rule version the current had been forked from (V2)
• The latest remote rule version we’re upgrading to(V4)

The algorithm should:

1. Return changes between R2 and V2
2. Return changes between V2 and V4
3. Return conflicts: fields modified in both R2 and V4. Or that information should be easily derived from the above.
4. Ignore insignificant changes, like changes in the order of rule tags

[elasticmachine]

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

[elasticmachine]

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

[banderror]

This PoC has been completed in #144060. Please read the description of this PR for the decisions, software design, and conclusions we've made.