fix: allow missing paths in OAS 3.1 if components or webhooks present

[probelabs]

Problem / Task

Fixes TT-16565. When importing an OAS 3.1 document with webhooks but no paths, it fails with "invalid paths: must be an object". In OpenAPI 3.1, the paths object is optional as long as either components or webhooks is present.

Changes

• Updated openapi3/openapi3.go to check if the OpenAPI version is 3.1.x and if components or webhooks are present before returning an error for missing paths.
• Added a failing test in openapi3/openapi3_test.go to verify that an OpenAPI 3.1 document with webhooks but no paths validates successfully.

Testing

• Added tests for OAS 3.1 missing paths but has components/webhooks.
• Ran go test ./... to verify all tests pass.