fix: simplify YAML anchor pattern in devproxy-errors.yaml

[waldekmastykarz]

Summary

Removes the unnecessary definitions: wrapper from devproxy-errors.yaml and promotes YAML anchors to top-level keys.

YAML anchors are a native language feature and don't need a JSON Schema/OpenAPI-style container. The schema already allows arbitrary top-level keys, so no schema changes are needed.

Before

definitions:
  client_error_body: &client_error_body
    message: "Client Error"
  server_error_body: &server_error_body
    message: "Server Error"

After

client_error_body: &client_error_body
  message: "Client Error"

server_error_body: &server_error_body
  message: "Server Error"

Closes #1568

[Copilot]

Pull request overview

This PR simplifies the YAML anchor pattern in DevProxy/devproxy-errors.yaml by removing the unnecessary definitions: wrapper object and promoting the YAML anchors (client_error_body, server_error_body) directly to top-level keys. This makes the file more idiomatic YAML — anchors are a native YAML language feature and do not need a JSON Schema/OpenAPI-style container. The v2.2.0 genericrandomerrorplugin.errorsfile.schema.json already has "additionalProperties": true at the root level, so the promoted keys are fully schema-compliant.

Changes:

• Removes the definitions: wrapper object from devproxy-errors.yaml
• Promotes client_error_body and server_error_body anchor definitions to top-level keys (reducing one level of indentation for each)

[garrytrinder]

Built and tested in detached mode with a config pointing to the YAML errors file. 1 error responses loaded from devproxy-errors.yaml — simplified top-level anchors work correctly. Schema has additionalProperties: true so the extra top-level keys are fine. LGTM.