Fix Incorrect response model for pods/{name}/log

The swagger spec for pods/{name}/log does not include
"text/plain" as a possible content-type for the the response.
So we implement ProducesMIMETypes to make sure "text/plain"
gets added to the default list ot content-types.

the v1.json was generated by running:
hack/update-generated-swagger-docs.sh;./hack/update-swagger-spec.sh;

Fixes #14071

api/swagger-spec/v1.json

@@ -8817,6 +8817,7 @@
        }
       ],
       "produces": [
+       "text/plain",
        "application/json",
        "application/yaml",
        "application/vnd.kubernetes.protobuf"