[Bexley] Add payment fallback script

[dracos]

For https://github.com/mysociety/societyworks/issues/4681 [skip changelog]

Doesn't actually include any Bexley specific tests/stuff, that should be added when payments are added in some other work. This is being used by Merton (and can be used by any SCP usage, which Bexley is).

[codecov]

Codecov Report

Attention: Patch coverage is 78.84615% with 11 lines in your changes missing coverage. Please review.

Project coverage is 82.33%. Comparing base (449245f) to head (5fd1b46).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
perllib/FixMyStreet/Roles/Cobrand/Paye.pm	71.42%	3 Missing and 3 partials ⚠️
perllib/FixMyStreet/Script/Waste/CheckPayments.pm	78.57%	1 Missing and 2 partials ⚠️
perllib/FixMyStreet/Script/Merton/SendWaste.pm	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5340      +/-   ##
==========================================
+ Coverage   82.30%   82.33%   +0.02%     
==========================================
  Files         425      426       +1     
  Lines       33518    33546      +28     
  Branches     5403     5406       +3     
==========================================
+ Hits        27587    27620      +33     
+ Misses       4333     4325       -8     
- Partials     1598     1601       +3     

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[dracos]

I've just pushed an extra commit on this to include apnReference support (as left by PAYE payments).