Set EnableExternalCloudController to true by default

[hakman]

This is not just about AWS, the OpenStack one for example is stable.
It means that someone should still enable the feature via spec.cloudControllerManager.cloudProvider, but no longer need to set the feature flag too.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: olemarkus

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [olemarkus]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[johngmyers]

There's little point to having a feature flag then. There's no point to disabling it. The only reason to keep it would be automated tests that need to work across multiple kOps versions.

[hakman]

I thought the procedure is to set it to true in case we want to flip it back in the next few weeks at least.

[johngmyers]

If the flag affected behavior beyond simply allowing options to be set, it would make sense to allow it to be turned back off. But this flag merely allows a field in the cluster spec to be non-nil.