Pin version of Sail used

[adam-cattermole]

We currently install from the https://github.com/maistra/istio-operator/tree/maistra-3.0 branch directly which results in any downstream changes potentially breaking our install (see #380). We should look to pin the version that we install alongside the image that we use.

That being said, it's worth considering that when installing from the community operators on OpenShift currently the only available build is the most recent nightly build. If we pin to a version and don't test frequently on OpenShift, changes could be made that would break our compatibility without our knowledge.

[adam-cattermole]

The release of the sail operator without a floating tag should be completed as part of OSSM-5547

[adam-cattermole]

For the time being while we are awaiting for a stable version of sail we will revert to local install defaulting to using istioctl. So that we are still aware of the changing requirements of sail without slowing down active development we can move the integration test (sail) to a nightly scheduled run instead of a hard requirement for PR's.

[adam-cattermole]

Until we find a way forward with #401 I'll pin to the latest nightly that still had the kustomize manifests.