fix: use accept header when fetching feed (#2737)
fix: use accept header when fetching feed (#2737)

* fix: use accept header when fetching feed

* fix: include atom too, and reuse constants from format classes

* add a catch all accept header
Riduidel/rss-bridge,RSS-Bridge/rss-bridge,RSS-Bridge/rss-bridge,ORelio/rss-bridge,Riduidel/rss-bridge,Riduidel/rss-bridge,ORelio/rss-bridge,RSS-Bridge/rss-bridge,ORelio/rss-bridge