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:
- origin: {F3688384}
- content: {F3688387}
- directory: {F3688388}
- release: {F3688389}
- revision: {F3688390}
- snapshot: {F3688392}
Colors and texts might still be improved.
Related to T2090
Depends on D2309