octavia-dashboard uses an incorrect region in specific multi-region deployments

[Gregory Thiemonge]

when using a multi-region deployment with:
- a centralized keystone in region0 (with endpoints to the public services of all the regions)
- per region keystone instances in region[1-2] (with endpoint to the services of their own region)

(region0 has endpoints for octavia in region1 and 2, region1 has an endpoint for octavia in region1, region2 for octavia in region2)

octavia-dashboard may fail to connect to the octavia service because it uses an incorrect region

in

https://github.com/openstack/octavia-dashboard/blob/979ee7f213b1cfc5a447c2b838e701c7a1358530/octavia_dashboard/sdk_connection.py#L47

the connection to the service uses "auth_url=request.user.endpoint"

this request.user.endpoint variable appears to be the auth endpoint of the horizon session (it is set when the user connects to horizon), this endpoint is not updated when the user selects another region in the Projects/Regions selector.
So if the user connects to horizon through region1 and then selects region2, octavia-dashboard looks for the octavia endpoint for region2 in the region1 catalog, and it fails with an error like:

keystoneauth1.exceptions.catalog.EndpointNotFound: publicURL endpoint for load-balancer service in region2 region not found

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/octavia-dashboard/+/925672