python3-sphinxcontrib-svg2pdfconverter: add new recipe

python3-sphinxcontrib-svg2pdfconverter: add new recipe

This will be a dependency for building the Yocto docs soon, so let's add
a recipe for it.

This does SVG to PDF (or PNG) conversion for images used in Sphinx
projects.

It exposes three different Sphinx extensions, each using a different
tool for the conversion:
- cairosvg, a Python module with no available recipe,
- inkscape, only available in seemingly unmaintained 3rd party layer,
- rsvg-convert,

So we'll only support the last extension for now.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>