Fix: Add Content-Type header to get-version-code command

- Added Content-Type: application/json header to POST request
- Expanded Accept header to include text/plain and */* for better compatibility
- Resolves 'Unsupported Media Type' error when calling get-version-code
- Added test case for get-version-code command

The fix ensures proper HTTP headers are sent for the getVersionCode operation,
which is a POST request with no body. Some Azure services require both
Content-Type and Accept headers to be present even for empty-body requests.

Author: Danny Tundwe (from Dev Box)

src/edge-action/azext_edge_action/aaz/latest/edge_action/version/_get_version_code.py

@@ -165,7 +165,10 @@ def query_parameters(self):
         def header_parameters(self):
             parameters = {
                 **self.serialize_header_param(
-                    "Accept", "application/json",
+                    "Content-Type", "application/json",
+                ),
+                **self.serialize_header_param(
+                    "Accept", "application/json, text/plain, */*",
                 ),
             }
             return parameters