Better sentry logging in MQTT message handler

[timcowlishaw]

Enabled Sentry's Sidekiq integration properly, and added some manual Breadcrumbs to better track what's going on in the MQTT message handler.

If we could get this to production when we meet next week so i can better understand those last few remaining errors from the upgrade, that'd be ace!

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ JSON::GeneratorError: Invalid Unicode [ff] at 0 app/lib/mqtt_messages_handler.rb in [] View Issue
• ‼️ JSON::GeneratorError: Invalid Unicode [04] at 22 app/lib/mqtt_messages_handler.rb in handle_topic View Issue
• ‼️ JSON::GeneratorError: Invalid Unicode [04] at 22 app/lib/mqtt_messages_handler.rb in handle_topic View Issue

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