[BUG] [Go] Optional values should be pointers

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

It is the same issue described in https://github.com/OpenAPITools/openapi-generator/issues/522. It was fixed for client, but not server.

openapi-generator version

7.16.0

OpenAPI declaration file content or url

---
openapi: 3.0.0
info:
  title: unset
  version: 0.1.0

paths:
  "/foo":
    get:
      summary: foo
      responses:
        '200':
          description: OK
          content:
            application/xml:
              schema:
                "$ref": "#/components/schemas/Bar"

components:
  schemas:
    Bar:
      properties:
        X:
          type: integer
        Y:
          type: integer
      required:
        - X

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/522 fixed it in the client.

Similar issue: https://github.com/OpenAPITools/openapi-generator/issues/22096

Start with the minimal OpenAPI declaration in the issue and reproduce the generated Go server output for schema Bar. Compare the server behavior with the client fix from issue 522, then inspect the Go server generation path. Done means optional schema properties are represented as pointers while required properties retain their required semantics.