fix(eppp): Add optional mqtt dependency

Author: david-cermak

components/eppp_link/examples/host/main/idf_component.yml

@@ -5,3 +5,7 @@ dependencies:
     override_path: ../../..
   console_cmd_ping:
     version: '*'
+  espressif/mqtt:
+    rules:
+    - if: idf_version >=6.0
+      version: ^1.0.0