[Security Solution][Rules] Require all fields to be accounted for in internal schema to response conversion

[marshallmain]

Summary

Closes #136910
Related to #136774

A major goal of the security solution rules schema refactor was to catch rule schema mistakes through static typing. Static types now identify many places where new fields need to be added: once a field is added in one place, e.g. the internal rules schema, type errors will appear in other places where the field needs to be handled. However, because the HTTP response schema defined optional fields as truly optional instead of required but possibly undefined, it was still possible to add an optional rule parameter to the rules schema without adding it to the conversion function between internal and response schemas.

This PR solves the issue by implementing a bit of custom logic to replace the use of t.partial when building the response schema. Instead, we take each of the optional fields and replace them with t.union([<optionalFieldSchema>, t.undefined]) so the runtime effect is the same - they're optional - but they must be explicitly set to undefined (or the valid field type) when building a response object.

To test this, try removing one of the optional params, e.g. event_category_override from typeSpecificCamelToSnake in rule_converters.ts. Prior to this PR there was no type error, but with this PR TS reports Property 'event_category_override' is missing in type ....

[elasticmachine]

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

[elasticmachine]

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

[e40pud]

lgtm

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: b587e01

Metrics [docs]

✅ unchanged

History

• 💔 Build #62889 failed cbcee1d
• 💔 Build #62464 failed 164e858
• 💔 Build #62180 failed d9f85ea
• 💚 Build #61845 succeeded 5afdd0b

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