refactor: move access request handling into own lib function

[Diaphteiros]

What this PR does / why we need it:
Previously, the lib/clusteraccess package had the CreateAndWaitForCluster method on the Manager interface, which created both, a ClusterRequest and an AccessRequest and waited for them to become ready. The logic that creates the AccessRequest and waits for it has been refactored out of the existing implementation and moved into a new WaitForClusterAccess method. This makes the code reusable for situations where the Cluster(Request) already exists.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:

Release note:

The `lib/clusteraccess` package's `Manager` interface has been expanded with the `WaitForClusterAccess` method, which creates/updates an `AccessRequest` for an existing `Cluster` or `ClusterRequest`.