[interop][cinder] review of next.json

Hello Interop WG,

We began a review of next.json [0] at yesterday's cinder meeting and a few issues came up.

1. The 'description' for the volumes capabilities should be updated; here's a patch:

https://review.opendev.org/c/osf/interop/+/789940

2. Are capabilities that require an admin (or system-scoped) token still excluded?

3. Are capabilities that require multiple users for testing (for example, volume transfer) excluded?

Thanks!

[0] https://opendev.org/osf/interop/src/branch/master/next.json