[backend] Added feature flag for Floating Action Button replacement

[Bonsai8863]

Proposed changes

• Added "FAB_REPLACEMENT" to default.json to ignore the ongoing FAB replacement tasking in non-development environments.

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case (coverage and e2e)
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

I am working to decompose #5269 into smaller PRs. This feature flag enables non-development environments to not be affected by efforts to replace the floating action button throughout the platform in the meantime.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.01%. Comparing base (e7b4870) to head (cd44830).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6738   +/-   ##
=======================================
  Coverage   68.01%   68.01%           
=======================================
  Files         538      538           
  Lines       65711    65711           
  Branches     5568     5568           
=======================================
  Hits        44691    44691           
  Misses      21020    21020           

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