This adds support for syncing ownership on Unixes and on Windows. The
scanner always picks up ownership information, but it is not applied
unless the new folder option "Sync Ownership" is set.

Ownership data is stored in a new FileInfo field called "OS data". This
is intended to hold further OS specific data in the future
(specifically, extended attributes), which is why the whole design is a
bit overkill for just ownership.

* main:
  gui, man, authors: Update docs, translations, and contributors
  cmd/syncthing/cli: Add show discovery command (fixes syncthing#8007) (syncthing#8378)
  gui, man, authors: Update docs, translations, and contributors
  lib/osutil: Only announce address of interfaces which are up (fixes syncthing#7458) (syncthing#8422)
  gui: Fix missing span end tag and missing nbsp semicolon in HTML (syncthing#8419)