Add a way to customize size of popup

[garyo]

I often get very large error message in eglot, and the flymake-posframe popup obscures most of my buffer. It would be great to be able to set max-height, and maybe also timeout. Locally I have this patch which just hardcodes the values I like:

modified   flymake-posframe.el
@@ -94,6 +94,8 @@ Only the `foreground' is used in this face."
 	   :internal-border-width 3
 	   :left-fringe 1
 	   :right-fringe 1
+           :max-height 20
+           :timeout 10
 	   :foreground-color (face-foreground 'flymake-posframe-foreground-face nil t)
 	   :background-color (face-background 'flymake-posframe-background-face nil t)
            :string (concat (propertize