Fix http_accept header in nginx.conf for docker install

[z01L]

The current nginx.conf in the english docker install doc has a very strict http_accept header check. It prevents other services in the Fediverse like Mastodon and Kbin federating with the Lemmy instance due to the way they send the http_accept header.

The change updates the http_accept header check and aligns it with the one in the ansible template.

[Daniel15]

I think this has to be updated in https://github.com/LemmyNet/lemmy/blob/main/docker/nginx.conf and https://github.com/LemmyNet/lemmy/blob/0.17.4/docker/prod/nginx.conf too? I'm not sure why there's multiple copies of the same Nginx config as it's easy for them to fall out of sync (and indeed the config in the 0.17.4 tag is quite a bit different to the one on the main branch)

[Nutomic]

True it would be good to fix that and consolidate the files in some way. Though the last link is from the release/0.17 branch, so it simply didnt have all the changes backported and wont be relevant once 0.18 is released.