Display a warning in the Extra fonts settings when HTTP in-use that Extra fonts won't work w/o HTTPS

[joshtrichards]

CODE doesn't support loading the fonts.json via HTTP, only HTTPS.

Refs:

• https://github.com/CollaboraOnline/richdocumentscode/blob/81dd7da881acc6d266dbe83a3a95963c91717dd3/proxy.php#L81-L87
• https://github.com/CollaboraOnline/online/blob/b5413f82743d89ce4996d824d7eb84fb9ca91cfb/wsd/COOLWSD.cpp#L1125 (both fonts and full remote configs both use RemoteJSONPoll() which has this requirement)

If someone is interested in implementing this, change will need to happen in here:

https://github.com/nextcloud/richdocuments/blob/f020d3904ccd3e00a534bbe9054df263c953dc53/src/components/AdminSettings.vue

[joshtrichards]

Fixed in #4273