pambackground, pamstretch-gen, pamstretch, pbmclean, pbmmask, pbmpage, pbmpscale: add pages (#12237)

* pambackground, pamstretch-gen, pamstretch, pbmclean, pbmmask, pbmpage, pbmpscale: add pages

* add missing linefeed

* Update pages/common/pamstretch.md

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

* Apply suggestions from code review

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

pages/common/pbmpage.md

@@ -0,0 +1,16 @@
+# pbmpage
+
+> Generate a test pattern for printing.
+> More information: <https://netpbm.sourceforge.net/doc/pbmpage.html>.
+
+- Generate a test pattern for printing onto US standard paper:
+
+`pbmpage > {{path/to/file.pbm}}`
+
+- Generate a test pattern for printing onto A4 paper:
+
+`pbmpage -a4 > {{path/to/file.pbm}}`
+
+- Specify the pattern to use:
+
+`pbmpage {{1|2|3}} > {{path/to/file.pbm}}`