pamnoraw, pamtopam, pamtopnm, pnmtoplainpnm, pnmtopnm, ppmtoppm: add pages (#11403)

* pamnoraw, pamtopam, pamtopnm, pnmtoplainpnm, pnmtopnm, ppmtoppm: add pages

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Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/common/ppmtoppm.md

@@ -0,0 +1,12 @@
+# ppmtoppm
+
+> Copy a PPM image.
+> More information: <https://netpbm.sourceforge.net/doc/ppmtoppm.html>.
+
+- Copy a PPM image (i.e. a PBM, PGM or PPM image) from `stdin` to `stdout`:
+
+`ppmtoppm < {{path/to/image.ppm}} > {{path/to/output.ppm}}`
+
+- Display version:
+
+`ppmtoppm -version`