[Observability] Use Observability rule type registry for list of rule types

[simianhacker]

Summary

This PR removes the static list of rule types, OBSERVABILITY_RULE_TYPES, by adding a list() method to the observabilityRuleTypeRegistry which returns a dynamic list of rules that are registered with Observability. This will prevent situations where solutions add new rules but they don't show up in the Observability rules manager because the author didn't realize they also needed to update OBSERVABILITY_RULE_TYPES.

[mgiota]

LGTM

[kibana-ci]

💚 Build Succeeded

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Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
observability	451.9KB	451.7KB	-222.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
observability	92.2KB	92.2KB	+30.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[mgiota]

@simianhacker I tested locally and I verify that only o11y rule types appear in the new o11y rules page