feat(resp): add option to disable XML serialization of errors

[CaselIT]

Fixes #2355

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (5ce771e) to head (a864d09).
Report is 1 commits behind head on master.

Additional details and impacted files

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##            master     #2356   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           64        64           
  Lines         7712      7721    +9     
  Branches      1267      1269    +2     
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+ Hits          7712      7721    +9     

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[vytas7]

Not directly related to this PR, but it seems we also need to update the wording of docs for App.set_error_serializer() regarding media handlers.

[vytas7]

Looks good, just the docs need a bit polish, and I would prefer another name for the option itself (but I don't have very good suggestions).

[vytas7]

LGTM now, thanks for this improvement 👍
We do want to get rid of any XML support out of the box, although we may want to add XML handlers in the future, either out of the box, or as a recipe, or an add-on library.

I would still like to polish docstrings and the proposed newsfragment, but I can try to address that in a followup PR.

Edit: got the ball rolling in #2358.