Null config for testing

[macta]

Simple proposal to slightly extend the NullConfigurationProvider with at:put: functionality so its easy to write tests for launchpad parameter conversion. Also has an example web server demonstrating a test.

While I could subclass NullConfigurationProvider in my own code, I'm hoping this change is non-controversial and hopefully shows others how they could easily write a similar test.

Understand if you prefer not to include this (and I can make my own subclass) but thought it might be interesting enough to include.

p.s. sorry for the extra changes - the change from P11 to P12 for category format type is annoying.

[codecov]

Codecov Report

❌ Patch coverage is 76.76056% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.97%. Comparing base (3611d90) to head (44cbfc7).
⚠️ Report is 22 commits behind head on release-candidate.

Files with missing lines	Patch %	Lines
...hpad-Examples/LaunchpadZnHelloApplication.class.st	52.17%	33 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##           release-candidate      #73      +/-   ##
=====================================================
- Coverage              99.79%   98.97%   -0.82%     
=====================================================
  Files                     62       64       +2     
  Lines                   3870     4011     +141     
=====================================================
+ Hits                    3862     3970     +108     
- Misses                     8       41      +33     

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