Add option to specify content header length

[benoit74]

Fix #320

To be reviewed / merged after #319

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.61%. Comparing base (8f79546) to head (f8fe4bc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
+ Coverage   84.57%   84.61%   +0.03%     
==========================================
  Files          14       14              
  Lines        1245     1248       +3     
  Branches      246      246              
==========================================
+ Hits         1053     1056       +3     
  Misses        149      149              
  Partials       43       43              

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[rgaudin]

LGTM but what I don't like here is that it's a magic option. There's no information about when this should be changed, why and how to figure out a better value.

[benoit74]

It's definitely kind of an expert value. But needs to be exposed in the Zimfarm so that it can be tweaked when needed.