fix(egress): expose more ranges as restricted rather than reserved (#39560) (#39624)

Backport #39560 by TheFox0x7

fixes: https://github.com/go-gitea/gitea/issues/39557

Signed-off-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

custom/conf/app.example.ini

@@ -536,7 +536,7 @@ INTERNAL_TOKEN =
 ;CONTENT_SECURITY_POLICY_GENERAL =
 ;;
 ;; Egress mode toggles between strictness of outgoing requests:
-;; Lax requires addresses to be allowed only if they are in private ranges, it allows all public ones
+;; Lax requires non-public targets (private, loopback, link-local, CGNAT and special-use ranges) to be allowed, it allows all public ones
 ;; Strict requires an explicit allow of all addresses
 ; EGRESS_MODE = lax
 ;;
@@ -551,10 +551,12 @@ INTERNAL_TOKEN =
 ;; a bracketed set of ports and ranges, | separated: *.mydomain.com:[80|443|3000-3010]
 ;; all ports: *.mydomain.com:*
 ;; A portless entry covers all ports in Lax mode, only 80 and 443 in Strict mode
-;; Port specs apply only where the list is consulted: in Lax mode that is private, loopback and CGNAT
-;; targets alone, public targets are allowed on every port whatever the list says. In Strict mode every
+;; Port specs apply only where the list is consulted: in Lax mode that is non-public targets alone,
+;; public targets are allowed on every port whatever the list says. In Strict mode every
 ;; target is checked, so ports restrict public hosts too.
-;; Reserved addresses like link-local and cloud metadata are denied
+;; Non-public targets need an IP or built-in entry, a host name entry alone never covers them.
+;; Reserved addresses (the IPv4-embedding NAT64, Teredo and 6to4 ranges, this-network, multicast and
+;; broadcast) are denied whatever the list says. To reach them configure an HTTP proxy
 ;; This list is enforced on direct connections only. When an HTTP proxy is configured, restricting the proxied target is the proxy server's responsibility.
 ;ALLOWED_HOST_LIST =