Rename Heptio Authenticator to AWS IAM Authenticator.

[niclic]

In light of the recent renaming of Heptio Authenticator to AWS IAM Authenticator for Kubernetes, now might be a good time to follow suit.

References:

• Renamed "Heptio Authenticator" to "AWS IAM Authenticator for Kubernetes"
• Renamed heptio-authenticator-aws -> aws-iam-authenticator

This PR is an initial attempt at this. Tests pass but I have not yet created a cluster from a local build.

The changes so far are cosmetic and some questions remain:

1. Should the spec change? If so, then to what?
   The AuthenticationSpec retains a key called Heptio of type HeptioAuthenticationSpec.

2. What about addon resources? See 1.
   The aws-iam-authenticator manifest(s) are in a directory called authentication.hept.io.

3. Binary has changed but no new docker image pushed as of yet.
   The docker image remains: gcr.io/heptio-images/authenticator:v0.3.0, so the binary will still be heptio-authenticator-aws. Updated images will likely be published very soon.

Original PR: #5197

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[k8s-ci-robot]

Hi @niclic. Thanks for your PR.

I'm waiting for a kubernetes 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.

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[niclic]

See also #5424

[k8s-ci-robot]

@niclic: PR needs rebase.

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[rifelpet]

duplicate of #5421 ?

[niclic]

Okay.