[Merton] Adds parks and open spaces layer

[MorayMySoc]

[Merton] Adds parks and open spaces layer

Layer contains parks that Merton not responsible for:
Wimbledon Common, Mitcham Common, Morden Hall Park
which have specific stoppers to guide to the right
place.

Only allowed to make a park report on a park or open
space on the layer for responsible parks.

Exceptional park Commons Extension Sports Ground is
in Kingston, but is responsibility of Merton so
can be selected from Merton Cobrand.

And Cypress tests

https://github.com/mysociety/societyworks/issues/4643
https://mysocietysupport.freshdesk.com/a/tickets/3934

Server config in same branch on servers

[skip changelog]

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 8 lines in your changes missing coverage. Please review.

Project coverage is 82.31%. Comparing base (287f7d2) to head (5e0bea5).

Files with missing lines	Patch %	Lines
perllib/FixMyStreet/Cobrand/Merton.pm	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5294      +/-   ##
==========================================
- Coverage   82.34%   82.31%   -0.04%     
==========================================
  Files         413      413              
  Lines       32719    32744      +25     
  Branches     5241     5242       +1     
==========================================
+ Hits        26942    26952      +10     
- Misses       4225     4240      +15     
  Partials     1552     1552              

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