🐛 allow EKS identity provider dissociation

[afarbos]

What type of PR is this?

/kind bug
What this PR does / why we need it:

Today it's impossible to disassociate the EKS identity provider since:

• if the configuration is null the reconciliation is skipped (the removed change)
• the disassociate only happen if the desired state is null, see https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/main/pkg/eks/identityprovider/plan.go#L59-L64

I believe https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/main/pkg/cloud/services/eks/identity_provider.go#L47 check is enough.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Checklist:

• squashed commits
• includes documentation
• includes emoji in title
• adds unit tests
• adds or updates e2e tests

Release note:

Allow to disassociate EKS identity provider 

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign justinsb for approval. For more information see the Code Review Process.

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

Needs approval from an approver in each of these files:

• OWNERS

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

[k8s-ci-robot]

Hi @afarbos. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[AndiDog]

Did you manually test this?

/assign