Add Allow-/Block-List for Migrate & Mirrors (#13610) (#13776)

* add black list and white list support for migrating repositories

* specify log message

* use blocklist/allowlist

* allways use lowercase to match url

* Apply allow/block

* Settings: use existing "migrations" section

* convert domains lower case

* dont store unused value

* Block private addresses for migration by default

* use proposed-upstream func to detect private IP addr

* add own error for blocked migration, add tests, imprufe api

* fix test

* fix-if-localhost-is-ipv4

* rename error & error message

* rename setting options

* Apply suggestions from code review

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

custom/conf/app.example.ini

@@ -1188,6 +1188,14 @@ QUEUE_CONN_STR = "addrs=127.0.0.1:6379 db=0"
 MAX_ATTEMPTS = 3
 ; Backoff time per http/https request retry (seconds)
 RETRY_BACKOFF = 3
+; Allowed domains for migrating, default is blank. Blank means everything will be allowed.
+; Multiple domains could be separated by commas.
+ALLOWED_DOMAINS =
+; Blocklist for migrating, default is blank. Multiple domains could be separated by commas.
+; When ALLOWED_DOMAINS is not blank, this option will be ignored.
+BLOCKED_DOMAINS =
+; Allow private addresses defined by RFC 1918, RFC 1122, RFC 4632 and RFC 4291 (false by default)
+ALLOW_LOCALNETWORKS = false
 
 ; default storage for attachments, lfs and avatars
 [storage]