Update paho-mqtt requirement from ~=1.6.1 to ~=2.0.0

Updates the requirements on [paho-mqtt](https://github.com/eclipse/paho.mqtt.python) to permit the latest version.
- [Release notes](https://github.com/eclipse/paho.mqtt.python/releases)
- [Changelog](https://github.com/eclipse/paho.mqtt.python/blob/master/ChangeLog.txt)
- [Commits](eclipse/paho.mqtt.python@v1.6.1...v2.0.0)

---
updated-dependencies:
- dependency-name: paho-mqtt
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -9,4 +9,4 @@ waitress~=2.1.2
 ipaddress~=1.0.23
 mock~=5.1.0
 coverage
-paho-mqtt~=1.6.1
+paho-mqtt~=2.0.0