Respond to handled errors using the accepted content-type (i.e. in RSS)

[gildesmarais]

Goal: Respond to handled errors using in the accepted content-type (i.e. in RSS).

Example Scenario:

• when an invalid feed is requested return a 404 rendering a response body using RSS/XML.
• When a config got deleted, respond with http 410 gone and provide helpful info for end-user debugging

Implementation idea:
hook into error handler, or investigate the use of https://roda.jeremyevans.net/rdoc/classes/Roda/RodaPlugins/TypeRouting.html

• the response should contain helpful information, but not reveal 'internals'
• The channel language must be changed to English
• if html2rss-config: provide description containing link to edit the config on Github
• Suggest to discuss on gh discussions