According to the discussion with DanielGibson, the default "20m" seems
too short. It would make LFS fail if the file is large / network is
slow.
I think relaxing this timeout doesn't have side affect. So change the
default value to 24h, IMO that should be long enough.
## ⚠️ BREAKING
If admins want the previous timeout, they should set the setting
`[server].LFS_HTTP_AUTH_EXPIRY`.
