Use the Jenkins colour palette

[janfaracik]

Would be good to hear your thoughts on this @uhafner -

Currently the Prism plugin uses its default colour palette which differs from the Jenkins palette. This PR looks to set the default theme to follow Jenkins' palette instead. This brings a couple of advantages:

• It looks more consistent with Jenkins
• Jenkins themes don't need to provide a theme for Prism as long as they override the default colour palette (Dark theme does this already for example, so we could remove .withProperty("prism-api", "theme", PRISM_THEME) from that plugin)

Before

After

(dark theme with the `prism-api` prop removed)

Testing done

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[uhafner]

Thanks for updating the colors, it totally makes sense to provide a Jenkins theme.

[uhafner]

Can you remove the assertion in the Test:

                .extracting(PrismTheme::getFileName)
                .isEqualTo("prism.css")

It actually does not verify anything useful and can be removed.

[janfaracik]

Done - want the entire assertion removed or just those two lines? Thanks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.39%. Comparing base (233dbfd) to head (ed0d489).
Report is 45 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #161      +/-   ##
============================================
- Coverage     75.59%   75.39%   -0.20%     
- Complexity       91       93       +2     
============================================
  Files            13       13              
  Lines           377      378       +1     
  Branches         30       30              
============================================
  Hits            285      285              
- Misses           89       90       +1     
  Partials          3        3              

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[uhafner]

Thanks!