Everything that goes through the volumes view builder
detail() method has a strict is_admin check on returning
the migration_status parameter [1]. This means the
migration_status parameter in the API reference should
be optional since it's admin-only and not always shown.
This fixes the v2 and v3 API references for showing,
creating, updating, resetting the status of, and creating
from a managed volume. As a result, the parameter for a
required migration_status parameter is unused and removed.
Note that there is no strict policy check on the
migration_status request parameter when resetting a volume's
status, but the action itself is admin-only by default
using the volume_extension:volume_admin_actions:reset_status
policy rule.
[1] https://opendev.org/openstack/cinder/src/tag/14.0.0/cinder/api/v2/views/volumes.py#L94
Change-Id: I82308dc1a6aaf039b675a17e19747f11be574209
Closes-Bug: #1828113
c549325bd2