MQTT settings and telemetry

[ryan-summers]

This PR replaces #242

This PR addresses #149 by exposing a simple MQTT-based settings interface

TODO:

• Resolve mutable ownership issues in the MqttInterface
• Expand settings interface to lockin.rs
• Add all settings (not yet supported by miniconf)
• Finalize and publish the miniconf package Deferred to the future.
• Move MqttInterface-like behaviors over to miniconf
• Move smoltcp-nal to a separate crate
• Test on hardware
• Implement stabilizer telemetry: Deferred to future

[jordens]

If there is an ergonomic advantage over using raw mqtt CLI utilities, let's also do a minimal CLI example client implementation for the IIR parameters in dual-iir.

[ryan-summers]

I have bench tested setting various values of dual-iir, such as the IIR y_offset parameter and the AFE gain. Everything appears to be in working order for merging.

[ryan-summers]

bors merge

[jordens]

bors r+

[bors]

Already running a review

[bors]

Build succeeded:

• compile (stable)
• style
• test (stable)