[WW] Add alt text to png for WasteWorks

[MorayMySoc]

Finish adding alt text for WasteWorks containers, but adding the png files

https://github.com/mysociety/societyworks/issues/5274

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.41%. Comparing base (47cf172) to head (0f65b88).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6015   +/-   ##
=======================================
  Coverage   83.40%   83.41%           
=======================================
  Files         500      500           
  Lines       37333    37335    +2     
  Branches     6166     6166           
=======================================
+ Hits        31138    31143    +5     
+ Misses       4387     4385    -2     
+ Partials     1808     1807    -1     

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