Add utip to the list of available contribution platforms

Please check if I did well with regexes

utip urls are formatted like so: https://utip.io/member_name https://utip.io/member_name/about https://utip.io/member_name/shop

retribute_api/providers.py

@@ -159,6 +159,14 @@ class ItchIo(BasicUsernameInDomainProvider):
 
     username_regex = r"^(\w+)\.itch\.io"
 
+@registry.register
+class Utip(BasicUsernameInDomainProvider):
+    id = "utip"
+    additional_ids = ["u-tip", "u tip"]
+    label = "utip"
+    url = "https://utip.io/tipoui"
+    username_regex = r"^utip\.io\/(\w+)"
+
 
 @registry.register
 class Custom(Provider):