change opacity to window.opacity for deprecation

alacritty/alacritty.yml

@@ -24,6 +24,7 @@
   #TERM: alacritty
 
 window:
+  opacity: 0.95
   # Window dimensions (changes require restart)
   #
   # Number of lines/columns (not pixels) in the terminal. The number of columns
@@ -339,7 +340,7 @@ colors:
 #
 # Window opacity as a floating point number from `0.0` to `1.0`.
 # The value `0.0` is completely transparent and `1.0` is opaque.
-background_opacity: 0.95
+#background_opacity: 0.95
 
 #selection:
   # This string contains all characters that are used as separators for