Implement scope support in debusine-client

In !1124 (merged), scope middleware makes use of a X-Debusine-Scope: scope-name http header to select the scope for an API call, defaulting to the DEBUSINE_DEFAULT_SCOPE setting if none is provided.

debusine-client needs to be updated to be scope aware:

Add a server-level configuration option in debusine-client to select the default scope.
Add a command line option in debusine-client to specify a different scope.
Send the X-Debusine-Scope header in API calls
Make sure we have a scope-aware client in testing and stable-backports before we drop support for unscoped API calls.

Edited Oct 10, 2024 by Sylvain Beucler

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information