openstackcli lacks user message API

[Lucio Seki]

User messages API was introduced on Cinder v3.3.
This is useful to retrieve, for instance, c-sch messages reporting some aync command errors:

$ cinder --os-volume-api-version 3.3 message-list
+--------------------------------------+---------------+--------------------------------------+-----------------------+-------------------------------------------------------------------------+
| ID | Resource Type | Resource UUID | Event ID | User Message |
+--------------------------------------+---------------+--------------------------------------+-----------------------+-------------------------------------------------------------------------+
| 3905775b-42d7-4293-b292-3cf5d928ed42 | VOLUME | e2e24cd7-21e6-4e32-808e-b0286f345289 | VOLUME_VOLUME_001_003 | schedule allocate volume:Could not find any available weighted backend. |
+--------------------------------------+---------------+--------------------------------------+-----------------------+-------------------------------------------------------------------------+

This support should also be added to Openstack CLI, so I could type:

$ openstack --os-volume-api-version 3 volume-message-list

and get the same output.