Add MQTT to constraints file (#38049)

homeassistant/package_constraints.txt

@@ -17,6 +17,7 @@ home-assistant-frontend==20200716.0
 importlib-metadata==1.6.0;python_version<'3.8'
 jinja2>=2.11.1
 netdisco==2.8.0
+paho-mqtt==1.5.0
 pip>=8.0.3
 python-slugify==4.0.0
 pytz>=2020.1

script/gen_requirements_all.py

@@ -297,8 +297,11 @@ def gather_constraints():
     return (
         "\n".join(
             sorted(
-                core_requirements()
+                {
-                + list(gather_recursive_requirements("default_config"))
+                    *core_requirements(),
+                    *gather_recursive_requirements("default_config"),
+                    *gather_recursive_requirements("mqtt"),
+                }
             )
             + [""]
         )