Add support for blockstoragev3 volumetype extra_spec operations
such as:
- create extra specs for volume type
- list all extra specs of volume type
- get specific extra spec of volume type
- update specific extra spec of volume type
- delete specific extra spec of volume type

In some conditions, Neutron will JSON-encode quota values as strings
instead of integers.

With this patch, the unmarshaling method is overridden to accept
integers as strings.

See https://bugs.launchpad.net/neutron/+bug/1918565

Fixes #2125

Keystone may include names into RoleAssignment entity, if provide include_names=true as query arguemnt

doc: https://docs.openstack.org/api-ref/identity/v3/index.html?expanded=id627-detail#id627

This is a documentation-only patch.

* The **baremetal** apiversions `doc.go` documented a non-existant
  "AllPages" method of `ListResult`.
* The **blockstorage** apiversions `doc.go` called `panic` with multiple
  arguments.
* The **sharedfilesystem** apiversions `doc.go` did not provide an
  example call.

ListAccesses: List accesses of private volume type
AddAccess: Add access of project to volume type
RemoveAccess: Remove access of project from volume type