Allow Forge instances to signal settings changes

[hardillb]

fixes #6126

Description

Has the settings component publish a MQTT message to signal to other forge app instances that a setting has changed.

Also sets up a topic subscription to receive these messages and reloads the value from the database.

Uses topic ff/v1/platform/sync and the commsClient uuid as the unique identifier.

Related Issue(s)

#6126

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

❌ Patch coverage is 35.71429% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.82%. Comparing base (6bec3e2) to head (5a8515f).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/comms/commsClient.js	0.00%	5 Missing ⚠️
forge/settings/index.js	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6128      +/-   ##
==========================================
- Coverage   76.85%   76.82%   -0.03%     
==========================================
  Files         381      381              
  Lines       19272    19286      +14     
  Branches     4641     4645       +4     
==========================================
+ Hits        14812    14817       +5     
- Misses       4460     4469       +9     

Flag	Coverage Δ
backend	76.82% <35.71%> (-0.03%)	⬇️

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