Create E2E tests for cluster registration on custom servers

[cnotv]

Detailed Description
Provide tests for cluster registration on custom server for both creation and import.

Context
As sequel of the CRUD E2E tests for clusters, a registration case is required.

It would require to fulfil the requirements for both cases.

Note: The displayed IP https://104.248.253.167 is actually a DO droplet used as remote Rancher instance.

Creation

Import

[gaktive]

We have added a few tests here for other automation requests so we have a good start. We may have to sweep through those and figure out what's missing so we can focus on specifics here to help whoever picks this up.