[Waste] WasteWorks specific offline fallback page

[struan]

Adds a waste specific offline fallback page at /offline/waste_fallback and updates the service worker to display this as a fallback if the path includes /waste.

Fixes #societyworks/4655

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 82.66%. Comparing base (c1291e0) to head (d941c12). :warning: Report is 27 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5767   +/-   ##
=======================================
  Coverage   82.66%   82.66%           
=======================================
  Files         456      456           
  Lines       35640    35639    -1     
  Branches     5813     5813           
=======================================
  Hits        29461    29461           
+ Misses       4485     4483    -2     
- Partials     1694     1695    +1     

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[dracos]

Oh, also there was https://github.com/mysociety/societyworks/issues/3745 if we wanted to tweak the wording of these pages to be more generic "problem with the network" perhaps

[struan]

Pushed an update to the fallback templates language.