Fix EKS encryption config value comparisons

[jon-fearer]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR addresses a couple of issues that are preventing EKS-managed clusters from fully reconciling when encryption is enabled:

• Update EncryptionConfig.Provider comparison to dereference pointers and compare KeyARN
• Fix a couple of other equality comparisons that were flipped (checking true vs false)
• Add assertions to TestCompareSlices (g.Expect(...) vs g.Expect(...).To(...))

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 #2908

Special notes for your reviewer:
This PR does not address the refactor work here, but I am happy to add that if it's still wanted.

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

Fix EKS encryption configuration comparison issues that blocked building a new cluster with encryption enabled

[k8s-ci-robot]

Hi @jon-fearer. Thanks for your PR.

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[sedefsavas]

/ok-to-test

[sedefsavas]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sedefsavas

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