Add links to MQTT docs

[hardillb]

part of #4707

Description

This adds some links to the MQTT docs for the Team Broker.

Also includes new user docs section to cover self hosted rather than just FFC

Related Issue(s)

Closes #4707

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.79%. Comparing base (0b4c35f) to head (799a95b).
Report is 35 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4775   +/-   ##
=======================================
  Coverage   78.79%   78.79%           
=======================================
  Files         311      311           
  Lines       14782    14782           
  Branches     3385     3385           
=======================================
  Hits        11647    11647           
  Misses       3135     3135           

Flag	Coverage Δ
backend	78.79% <ø> (ø)

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[hardillb]

@joepavitt Can you please cast an eye over this and merge if happy