[DX-2179] docs: fix Content-Type in Swagger for Streams API endpoints (#1118)

(cherry picked from commit 44d4459)

Author: buger

swagger/dashboard-swagger.yml

@@ -1988,7 +1988,7 @@ paths:
             enum: ["application/vnd.tyk.streams.oas"]
       requestBody:
         content:
-          application/json:
+          application/vnd.tyk.streams.oas:
             examples:
               StreamsAPIExample:
                 $ref: "#/components/examples/streamsExample"
@@ -2240,7 +2240,7 @@ paths:
         - $ref: '#/components/parameters/Authentication'
       requestBody:
         content:
-          application/json:
+          application/vnd.tyk.streams.oas:
             examples:
               PatchOASExample:
                 $ref: "#/components/examples/streamsExample"
@@ -2333,7 +2333,7 @@ paths:
             type: string
       requestBody:
         content:
-          application/json:
+          application/vnd.tyk.streams.oas:
             examples:
               StreamsAPIExample:
                 $ref: "#/components/examples/streamsExample"