Add addoption by annotation feature

[michaelhtm]

Issue #, if available:

Description of changes:
These changes introduce a new feature gate called ResourceAdoption
which allows users to provide the Read required fields in the annotation and
an empty spec, and the controller would populate the resource and adopt
from AWS

Currently we are considering two values for the adoption-policy annotation,
one being adopt, which will just try to adopt a resource, and if not found,
keep trying until a resource to adopt exists, or adopt-or-create which will
be able to create a resource if adoption fails because resource doesn't exist.

Before we support adopt-or-create we need a solution in code-gen
where we change how we handle the PopulateResourceFromAnnotation
which currently only allows the population of fields that are
required for a readOne operation, and they happen to be all scalar
fields (besides ARN, but we have a way of handling that), but the
required fields for create would need to be sometimes structs,
and this would require users to provide values in form of maps
eg.
Creating an EKS cluster requires a ResourceVPCConfig, which is a
struct that contains subnetIDs etc.
We can have a couple of ways to address this.

1. Accept these values in the spec, and return terminal error when
   we attempt a create and the create required fields are not provided
2. Accept these values in the adoption-fields annotation. This would
   need a code-gen change to allow reading from structs and assigning
   fields. but it would also make the annotation easy to make mistakes
   with when using yaml

Here's an example for cluster:

apiVersion: eks.services.k8s.aws/v1alpha1
kind: Cluster
metadata:
  name: my-cluster
  annotations:
    services.k8s.aws/adoption-policy: "adopt"
    services.k8s.aws/adoption-fields: | 
        {
          "name": "my-cluster"
        }

Here's another one to adopt a nodegroup

apiVersion: eks.services.k8s.aws/v1alpha1
kind: NodeGroup
metadata:
  name: my-ng
  annotations:
    services.k8s.aws/adoption-policy: "adopt"
    services.k8s.aws/adoption-fields: | 
        {
          "name": "ng-12324",
          "clusterName": "my-cluster"
        }

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[a-hilaly]

Great work on this Mr Michael! i left a few comments below

[a-hilaly]

🚀

[ack-prow]

@michaelhtm: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
verify-attribution	4d78380	link	false	/test verify-attribution
ecr-controller-test	4d78380	link	true	/test ecr-controller-test
s3-controller-test	4d78380	link	true	/test s3-controller-test
iam-controller-test	4d78380	link	true	/test iam-controller-test

Full PR test history. Your PR dashboard.

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[a-hilaly]

Great work on this Michael! merging to see how tests are doing on code-gen
/lgtm

[ack-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: a-hilaly, michaelhtm

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