[NEW] rancher2_cloud_credential resource for opentelekomcloud

[anton-sidelnikov]

Is your feature request related to a problem? Please describe.

Need to add cloud credential for opentelekomcloud

Additional context

Please check next docu:
https://registry.terraform.io/providers/rancher/rancher2/latest/docs/resources/cloud_credential

Need to add cloud credential for opentelekomcloud, i assume that we can reuse openstack code for user/pass auth.
In final we should implement:

• user/pass auth
• cloud.yaml auth
• ak/sk auth

auth also can be reused from here https://github.com/opentelekomcloud/gophertelekomcloud in openstack/loader.go