imagemagick: update pages (#12874)

* compare, convert, identify, import, mogrify, montage:
   move pages to subcommands of `magick`, create alias pages

* convert: add deprecation notice

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/magick-compare.md

@@ -0,0 +1,13 @@
+# magick compare
+
+> Create a comparison image to visually annotate the difference between two images.
+> See also: `magick`.
+> More information: <https://imagemagick.org/script/compare.php>.
+
+- Compare two images:
+
+`magick compare {{path/to/image1.png}} {{path/to/image2.png}} {{path/to/diff.png}}`
+
+- Compare two images using the specified metric:
+
+`magick compare -verbose -metric {{PSNR}} {{path/to/image1.png}} {{path/to/image2.png}} {{path/to/diff.png}}`