Fix ObjectMeta CRD validation

[mikkeloscar]

As mentioned in #241 the CRD validation for the ObjectMeta fields which we used in various places doesn't work because the schema is just object for the whole metadata field so anything below is dropped.

This PR aims to fix the problem in two ways.

1. Introduce a new type EmbeddedObjectMetaWithAnnotations which is a slimmed down version of metav1.ObjectMeta that only has Annotations as a field. This has the bonus of only exposing the field which is actually used by the stackset controller for various sub resources e.g. setting a custom annotation on the ingress or service resources (Labels are not used, so no need to allow users to set them for instance).
2. It uses a patched version of https://github.com/kubernetes-sigs/controller-tools based on this PR: ⚠️ Only prevent validation of top-level ObjectMeta field kubernetes-sigs/controller-tools#395. (I have made a fork and are pulling it from there: mikkeloscar/controller-tools@54e4525, I'm open for suggestions on how to better manage this).
3. Introduce a new type EmbeddedObjectMeta which is a slimmed down version of metav1.ObjectMeta that has Labels and Annotations. This is used for a newly defined PodTemplateSpec type which is similar to v1.PodTemplateSpec but has EmbeddedObjectMeta instead of metav1.ObjectMeta.

Additionally it drops metav1.ObjectMeta from the HorizontalPodAutoscaler field. This is not in use in the code, so it doesn't make sense to support users setting it. We may want to add it in the future as annotations may be needed for interacting with https://github.com/zalando-incubator/kube-metrics-adapter but we have the Autoscaler field supporting this already. I would like to refactor the HorizontalPodAutoscaler field anyway in the future.

[aermakov-zalando]

What about labels? Do we support those?

[coveralls]

Pull Request Test Coverage Report for Build 1696

• 17 of 23 (73.91%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.07%) to 68.607%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/core/stack_resources.go	17	23	73.91%

Files with Coverage Reduction	New Missed Lines	%
pkg/core/stack_resources.go	1	90.74%

Totals
Change from base Build 1633:	-0.07%
Covered Lines:	1556
Relevant Lines:	2268

---

💛 - Coveralls

[muaazsaleem]

Labels are not used, so no need to allow users to set them for instance

@aermakov-zalando ^ from the issue description

[aryszka]

👍

[mikkeloscar]

Deployments are failing with this in place:

Need to adjust the ObjectMeta of the PodTemplate.

Updated the PR description with the fixes that was done.

[mikkeloscar]

👍

[muaazsaleem]

👍