feat(amneziawg): support persistent keepalive ranges (#6881)

AmneziaWG clients accept a randomised PersistentKeepalive range such as 15-25,
which makes keepalive timing harder to fingerprint; the panel only stored a
single number. A client's keepalive may now be a range, validated the way
AmneziaWG parses it. The downloadable .conf and vpn:// profile carry the range,
Clash/Mihomo output gets its lower bound, and plain WireGuard stays scalar-only.
The range lives in an additive wg_keep_alive_range column, so the integer
column and an older panel binary keep working after a rollback.

tools/openapigen/schema.go

@@ -31,12 +31,13 @@ type Field struct {
 }
 
 type TypeRef struct {
-	Kind    TypeKind
-	Name    string
-	Element *TypeRef
-	Key     *TypeRef
-	Value   *TypeRef
-	Inner   *TypeRef
+	Kind     TypeKind
+	Name     string
+	Element  *TypeRef
+	Key      *TypeRef
+	Value    *TypeRef
+	Inner    *TypeRef
+	Variants []TypeRef
 }
 
 type TypeKind string
@@ -48,6 +49,7 @@ const (
 	KindBool    TypeKind = "boolean"
 	KindArray   TypeKind = "array"
 	KindMap     TypeKind = "map"
+	KindUnion   TypeKind = "union"
 	KindObject  TypeKind = "object"
 	KindRef     TypeKind = "ref"
 	KindUnknown TypeKind = "unknown"