Update paho-mqtt requirement from ~=1.6.1 to ~=2.1.0

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/paho.mqtt.python@v1.6.1...v2.1.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -9,4 +9,4 @@ waitress~=3.0.0
 ipaddress~=1.0.23
 mock~=5.1.0
 coverage
-paho-mqtt~=1.6.1
+paho-mqtt~=2.1.0