Add endpoints /badge/(object_type)/(object_id)/ and /badge/(object_pid)/
to generate Github style like SVG badges for linking to the archive in
a README file.
Those new endpoints add CORS header to the HTTP responses in order to be
used from a different domain than *.softwareheritage.org ones.
Below is a preview of the generated badges according to swh object type:
Colors and texts might still be improved.
Related to T2090