Filesystem Revamp

[askvortsov1]

Functionality Discussion

Related:
#1783
#984
#822

Is your feature request related to a problem? Please describe.
We currently use a very patchwork way of managing and accessing the filesystem from within flarum. Sometimes, like in avatar uploads, we use Flysystem, other times we explicitly use a local file system. Regardless, there is very little centralization, and the whole thing is built somewhat haphazardly. I think we should build a system that will abstractify filesystem access across the site, which could be built on to allow configuration/management of storage options in config.php or the admin dashboard.

Describe the solution you'd like
It looks like @luceos has started a pretty cool approach in https://github.com/FriendsOfFlarum/filesystem-drivers

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. We do this to keep the amount of open issues to a manageable minimum.
In any case, thanks for taking an interest in this software and contributing by opening the issue in the first place!

[askvortsov1]

Duplicate of #1783