feat: Add APIMethod asset type with request/response schemas

[Tony-Atlan]

Summary

• Adds APIMethod Java SDK type (IAPIMethod.java, APIMethod.java, _overlays/APIMethod.java) as a child of APIPath with request/response schema relationships
• Updates APIPath and APIObject SDK types with new relationship fields (apiMethods, apiMethodsRequestingThis, apiMethodsRespondingWithThis)
• Updates OpenAPI Spec loader to create APIObject, APIField, and APIMethod assets from OpenAPI specifications:
  • Phase 1: Creates APIObject per components/schemas entry, APIField per schema property, with $ref handling for nested object references
  • Phase 2: Creates APIMethod per HTTP operation per path, with request/response blobs for display and structured relationships to APIObject for field-level search
  • Phase 3: Creates synthetic APIObject + APIField assets for inline schemas with properties
• All existing APISpec/APIPath behavior preserved unchanged (backward compatible)

Tickets

• EPD-268 — Augment OpenAPI Spec API Assets with Request, Response and Parameters
• PRDLNCH-5559 — Include APIMethod as a child of APIPath

Test plan

• Verify compilation passes
• Verify existing Petstore tests still pass (connectionCreated, specCreated, pathsCreated)
• Verify new tests pass (objectsCreated, fieldsCreated, methodsCreated, methodRequestSchemaLinked, methodResponseSchemaLinked, objectRefFieldsLinked)
• Run against a live Atlan tenant with sample OpenAPI specs to confirm asset creation
• Verify APIMethod assets appear in the UI with request/response blobs on the overview page

🤖 Generated with Claude Code

[cmgrote]

The only bit that should be direct-managed here is the _overlays/ — everything else needs to go via models repo first.

[Tony-Atlan]

Thanks for the feedback. Understood — the SDK types (IAPIMethod.java, APIMethod.java, and relationship changes to IAPIPath/IAPIObject/APIPath/APIObject) should be generated from the models repo, not hand-written here.

The models PR is up at https://github.com/atlanhq/models/pull/1933 with the APIMethod entity def and 3 relationship defs. Once that's merged and the SDK generator runs, the auto-generated types will replace the hand-written ones in this PR.

For now, the loader code (OpenAPISpecLoader.kt + tests) directly imports com.atlan.model.assets.APIMethod, so removing the SDK files would break compilation. The plan is:

1. Merge the models PR (Bump dependencies #1933)
2. Run the SDK generator to produce the official types
3. Rebase this PR to drop the hand-written SDK files, keeping only _overlays/APIMethod.java + loader code

The _overlays/APIMethod.java (creator method) is the only manually-authored SDK file that should remain.