UI: Add IPv4 / IPv6 selection setting

This commit adds a field in Settings -> Advanced called
'IP Address Family' that allows users to select IPv4 and
IPv6, IPv4 Only, or IPv6 Only.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f