gouldtoppm, mtvtoppm, pamstack: add pages (#12262)

* gouldtoppm, mtvtoppm, pamstack: add pages

---------

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

pages/common/gouldtoppm.md

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+# gouldtoppm
+
+> Convert a Gould scanner file to a PPM image.
+> More information: <https://netpbm.sourceforge.net/doc/gouldtoppm.html>.
+
+- Convert a Gould scanner file to a PPM image:
+
+`gouldtoppm {{path/to/file.gould}} > {{path/to/output.ppm}}`

pages/common/mtvtoppm.md

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+# mtvtoppm
+
+> Convert an MTV or PRT ray tracer file to a PPM image.
+> More information: <https://netpbm.sourceforge.net/doc/mtvtoppm.html>.
+
+- Convert an MTV or PRT ray tracer file to a PPM image:
+
+`mtvtoppm {{path/to/file.mtv}} > {{path/to/output.ppm}}`

pages/common/pamstack.md

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+# pamstack
+
+> Stack the planes of multiple PAM images into one PAM image.
+> More information: <https://netpbm.sourceforge.net/doc/pamstack.html>.
+
+- Stack the planes of the specified PAM images in the specified order:
+
+`pamstack {{path/to/image1.pam path/to/image2.pam ...}} > {{path/to/output.pam}}`
+
+- Specify the tuple type name of the output PAM file (maximum of 255 characters):
+
+`pamstack -tupletype {{tuple_type}} {{path/to/image1.pam path/to/image2.pam ...}} > {{path/to/output.pam}}`