feat: RND-72: Add vendor extensions support in openapi autoschema

[niklub]

drf-yasg default SwaggerAutoSchema doesn’t provide a way to include custom extensions in the generated openapi.json.

For example, we need to produce the following path to be able to use idiomatic method naming with fern

paths:
  "/api/annotations/{id}/":
    get:
      x-fern-sdk-group-name: annotations
      x-fern-sdk-method-name: get
      operationId: api_annotations_read
      summary: Get annotation by its ID
      description: Retrieve a specific annotation for a task using the annotation result ID.
      responses:
        "200":
          description: ""
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Annotation"
      tags:
        - Annotations

Proposed solution:

• Extend SwaggerAutoSchema to include extra operation without modifying the names

• Allow base settings config to specify vendor extensions prefixes

Additional changes

• openapi 3.0 incompatible namings in some paths
• example of using x-fern in annotations.get

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.97%. Comparing base (c7b4b98) to head (c216587).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5908      +/-   ##
===========================================
+ Coverage    75.96%   75.97%   +0.01%     
===========================================
  Files          159      160       +1     
  Lines        13385    13396      +11     
===========================================
+ Hits         10168    10178      +10     
- Misses        3217     3218       +1     

Flag	Coverage Δ
pytests	75.97% <100.00%> (+0.01%)	⬆️

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