esim/http_json_api.py: support text/plain response Content-Type

Allow returning text/plain Content-Types as 'data' output argument.

So far, all the esim/http_json_api functions require a JSON response.
However, a specific vendor has a list function where the request is JSON
but the response is text/plain CSV data. Allow and return in a dict.

Change-Id: Iba6e4cef1048b376050a435a900c0f395655a790

pySim/esim/http_json_api.py

@@ -411,20 +411,30 @@ class JsonHttpApiClient():
         # SGP.22, section 6.5.1)
         if response.status_code != self.api_func.expected_http_status:
             raise HttpStatusError(response)
-        if response.content and not response.headers.get('Content-Type').startswith(req_headers['Content-Type']):
+
+        resp_content_type = response.headers.get('Content-Type')
+        if response.content and not resp_content_type.startswith(req_headers['Content-Type']):
             raise HttpHeaderError(response)
+
         if not response.headers.get('X-Admin-Protocol', 'gsma/rsp/v2.unknown').startswith('gsma/rsp/v2.'):
             raise HttpHeaderError(response)
 
         # Decode response and return the result back to the caller
         if response.content:
-            output = self.api_func.decode_client(response.json())
+            if resp_content_type.startswith('application/json'):
+                output = self.api_func.decode_client(response.json())
+            elif resp_content_type.startswith('text/plain;charset=UTF-8'):
+                output = { 'data': response.content.decode('utf-8') }
+            else:
+                raise HttpHeaderError(f'unimplemented response Content-Type: {response.headers=!r}')
+
             # In case the response contains a header, check it to make sure that the API call was executed successfully
             # (the presence of the header field is checked by the decode_client method)
             if 'header' in output:
                 if output['header']['functionExecutionStatus']['status'] not in ['Executed-Success','Executed-WithWarning']:
                     raise ApiError(output['header']['functionExecutionStatus'])
             return output
+
         return None
 
 class JsonHttpApiServer():