Improve Nginx http accept regex

[melroy89]

• Combined the multiple valid accept headers into the same regex line (so we don't constantly need 3 lines), hence the (?:...|...|...) group
• Be robust for an array of HTTP Accept headers (normally comma separated). Like Mastodon and Friendica is using, solving issue: ActivityPub services are using multi accept headers #1385 . Hence the additional .* regex.

Now all the AP requests are indeed getting logging correctly to the mbin_instance.log instead of the mbin_access.log (some examples below):

38.242.251.94 - - [19/Jan/2025:15:48:08 +0100]  "POST /f/inbox HTTP/1.1" 200 12 "-" "PeerTube/7.0.1 (+https://tilvids.com)" "kbin.melroy.org" 0.007
143.244.172.205 - - [19/Jan/2025:15:43:40 +0100]  "POST /f/inbox HTTP/1.1" 200 12 "-" "undefined/undefined (+http://a.gup.pe)" "kbin.melroy.org" 0.097
103.184.175.1 - - [19/Jan/2025:15:47:48 +0100]  "GET /f/object/66dfdf6f-9ca4-4c65-a754-9ea2015d787d HTTP/1.1" 200 12 "-" "Mastodon/4.4.0-mastau.1 (http.rb/5.2.0; +https://mastodon.au/)" "kbin.melroy.org" 0.004
178.21.23.139 - - [19/Jan/2025:15:48:13 +0100]  "GET /f/object/66dfdf6f-9ca4-4c65-a754-9ea2015d787d HTTP/1.1" 200 12 "-" "Akkoma 3.13.3-0-g963467f; https://fe.disroot.org <[email protected]>" "kbin.melroy.org" 0.005
65.109.234.6 - - [19/Jan/2025:15:47:31 +0100]  "GET /f/object/66dfdf6f-9ca4-4c65-a754-9ea2015d787d HTTP/1.1" 200 12 "-" "http.rb/5.1.1 (Mastodon/4.2.10; +https://mstdn.business/)" "kbin.melroy.org" 0.004
66.148.120.148 - - [19/Jan/2025:15:48:37 +0100]  "POST /i/inbox HTTP/1.1" 200 12 "-" "http.rb/5.1.1 (Mastodon/4.1.21; +https://mastodon.sdf.org/)" "kbin.melroy.org" 0.007
54.38.146.69 - - [19/Jan/2025:15:48:40 +0100]  "POST /i/inbox HTTP/1.1" 200 12 "-" "http.rb/5.1.1 (Mastodon/4.2.15; +https://mastodonapp.uk/)" "kbin.melroy.org" 0.007

Fixes: #1385

[melroy89]

Tested and works now on my server (logs). And fixes indeed the issue.