Split live-status tracking into its own subscriber (and share one MQTT connection) - Part 2: Add LiveStatusSubscriber

[n-lark]

Description

Gives live status its own LiveStatusSubscriber instead of bundling it into the team-channel subscriber, and has the two share one team MQTT connection (using the attach/detach from PR 1) rather than each needing its own.

Cut from #7843

See test plan: #7608 (comment)

Related Issue(s)

Resolves #7608

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
• Link to Changelog Entry PR, or note why one is not needed.

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 75.61%. Comparing base (e01772b) to head (91a07e2).

Additional details and impacted files

@@                     Coverage Diff                      @@
##           7608-mqtt-shared-connection    #7844   +/-   ##
============================================================
  Coverage                        75.61%   75.61%           
============================================================
  Files                              432      432           
  Lines                            23035    23035           
  Branches                          6107     6107           
============================================================
  Hits                             17417    17417           
  Misses                            5618     5618           

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backend	75.61% <ø> (ø)

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[cstns]

Looks good to me. The only thing i'd like to touch base on is the naming issue I mentioned on the pr this is based off of.

Other than that, happy to merge