[REQ] [GO] Support yaml endpoints

Is your feature request related to a problem? Please describe.

My API has two kinds of endpoints, most of them use application/json but a few rely on text/x-yaml. As it is today, we are forced to override the generated code in order to decode the request and encode the response properly for a YAML endpoint. It would be extremely helpful if the generator could generate code that supports encoding/decoding YAML.

Describe the solution you'd like

Be able to define an endpoint that accepts text/x-yaml and the go-server generator can generate an endpoint implementation capable of encoding/decoding YAML.

Describe alternatives you've considered

So far we could only achieve this by replacing the handler function for each YAML route, but this is not a good approach, it would be nice to have it out of the box.

Example of what we are doing:

routes[c.getRouteIndex("GetRunResultJUnit")].HandlerFunc = c.GetRunResultJUnit
routes[c.getRouteIndex("GetTestVersionDefinitionFile")].HandlerFunc = c.GetTestVersionDefinitionFile

Additional context

Example of endpoint:

/test.yaml:
    put:
      tags:
        - definition
      summary: Update a test using its definition 
      operationId: updateTestDefinition
      requestBody:
        content:
          text/x-yaml:
            schema:
              type: object
              properties:
                id:
                  type: string
                name:
                  type: string
                # rest of the properties
      responses:
        200:
          description: Test updated successfully

Start by locating the go-server generator's handling of request and response content types, then compare it with the generated JSON handler paths and the route HandlerFunc overrides shown in the issue. Done means an endpoint declaring text/x-yaml can use generated code to decode requests and encode responses without replacing its handler manually.