Insights API: resource results endpoint, schema updates, and fixes

Changes

New:

POST /insights/v1/results/source/{sourceID}/insight/{insightKey}/resource-results: Replaces all resource results for the specified insight. Any existing unresolved resource results not present in the new set will be removed.

Changed:

POST /insights/v1/results/source/{sourceID}/insight/{insightKey} now accepts metadata only. The resourceResults field was removed from the request body. Use the new resource-results POST above.
status and dismissalDetails can be set on the same Insights POST request. Making a separate status call optional.
GET Insights request responses now include dismissalDetails (dismissal reason and comment) for read-back and verification.
Request/response schemas are split: writable request types are separate from response types, so server-computed fields (severity, resolved, enhancement, etc.) are not documented as client-writable.

Deprecated:

PUT /insights/v1/results/source/{sourceID}/insight/{insightKey}/status: Still supported, but deprecated. Replaced by setting status and dismissalDetails on the POST calls.

Fixed:

Resource result updates now persist result_type, location, resource_type, account, and provider.
externalUrl prefers a user-provided URL and falls back to the auto-generated ARN URL when unset.
Declarative resource-results writes no longer delete existing data if the upsert step fails.