docs: user management: avoid some inconsistencies

docs: user management: avoid some inconsistencies

The space between '--' and 'path' in two of the commands was wrong. The other
changes make the names of the store and token consistent with the rest of the
section and should improve readability.

Also add the Datastore.Verify permission in the output of the command:
proxmox-backup-manager user permissions john@pbs --path /datastore/store1
A DatastoreAdmin now has this permission and that's what john@pbs is in the
example.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>