Add support for custom ZIM illustration

[benoit74]

Fix #79

Nota: I consider that this code should ultimately make its way to the python-scraperlib since it is a very generic way to handle ZIM illustration which probably matches most scraper needs. Could even be hidden behind the DefaultIllustrationMetadata which could accept a string as well as input and if such consider that it is the path or URL to illustration to use.

[codecov]

Codecov Report

Attention: Patch coverage is 55.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 43.13%. Comparing base (e1b706e) to head (91f696a).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/src/fcc2zim/scraper.py	55.55%	5 Missing and 3 partials ⚠️
scraper/src/fcc2zim/entrypoint.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
==========================================
+ Coverage   42.77%   43.13%   +0.36%     
==========================================
  Files           9        9              
  Lines         339      357      +18     
  Branches       45       49       +4     
==========================================
+ Hits          145      154       +9     
- Misses        193      199       +6     
- Partials        1        4       +3     

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[rgaudin]

LGTM ; and I agree it should eventually move to scraperlib