Add option background_image_anchor to configure bgimage position

kitty/options/parse.py

@@ -57,6 +57,14 @@ class Parser:
     def background_image(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['background_image'] = config_or_absolute_path(val)
 
+    def background_image_anchor(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
+        val = val.lower()
+        if val not in self.choices_for_background_image_anchor:
+            raise ValueError(f"The value {val} is not a valid choice for background_image_anchor")
+        ans["background_image_anchor"] = val
+
+    choices_for_background_image_anchor = frozenset(('northwest', 'north', 'northeast', 'east', 'southeast', 'south', 'southwest', 'west', 'center'))
+
     def background_image_layout(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         val = val.lower()
         if val not in self.choices_for_background_image_layout: