This patch implements API part to the feature of exposing conductors
information.
A new API object Conductor is added to provide endpoints below:
* GET /v1/conductors for listing conductor resources
* GET /v1/conductors/{hostname} for showing a conductor
V1 endpoint discovery and default policy are updated.
A conductor field is added to Node API object, which returns in
/v1/nodes* related endpoints.
Considering patch size and microversion conflicting with other api
patches, api-ref would go in another patch if no strong opinions.
Story: 1724474
Task: 28064
Change-Id: Iec6aaabc46442a60e2d27e02c21e67234b84d77b
7c7744dfb3