Currently passing a sha1 as url argument to the webapp endpoints works only if it is in lowercase form.

If a sha1 is passed in uppercase form, we end up in a 404 error page (see [1] for instance).

For commodity of use, we should support passing sha1s in uppercase form but also with
mixed uppercase and lowercase parts.

Redirecting to the lowercase sha1 endpoints when such cases are encountered seems the
right way to implement this.

[1] https://archive.softwareheritage.org/browse/snapshot/1A8893E6A86F444E8BE8E7BDA6CB34FB1735A00E/