Optionally return full role arn including path during token verification

[terricain]

What this PR does / why we need it: When creating EKS nodegroups where the node's IAM role contains a path, the nodes fail to join the cluster. This adds the ability to look up a role's full ARN including the path and return that when verifying a token.

The reason this is needed is because the assume-role ARN that is returned by sts.get-caller-idendentity does not include the IAM role's path.

I've added a "role cache" which calles iam.list-roles and stores a mapping between the roles unique role ID and the full ARN, as the UserID returned by sts.get-caller-identity contains the roles unique ID therefore looking up the existing role's correct ARN is possible.

This does require the clusters IAM role to have the iam:ListRoles action. If the role cache gets an error when calling list roles and its not a transient error, it'll disable all future lookups and the functionality will revert to the original behaviour. I figured it would be better to make this more an opt in rather than a requirement as else it might just break nodes joining a cluster whenever its released.

Which issue(s) this PR fixes:
Fixes #268
Fixes #153

[linux-foundation-easycla]

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• ✅ login: terrycain / name: Terry Cain (885868b)

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[terricain]

@dims / @nckturner / @nnmin-aws can we get a review on this please?

[nnmin-aws]

/test

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/test all

[terricain]

Thanks @nnmin-aws the tests seem to have passed, what now?

[terricain]

@nnmin-aws @dims @nckturner what else is required for this PR? There's been no progress for nearly 2 months, some guidance would be appreciated.

[dims]

cc @cartermckinnon

[nnmin-aws]

@terrycain @dims apology for the delay! i am so sorry about it. We were hesitating at the change because it requires additional invocation of aws IAM and might increase latency of authN.

There is another PR actually merged https://github.com/kubernetes-sigs/aws-iam-authenticator/pull/670/files#diff-5de38ab8d77d935766314beeb9a9e3b7165eb470e656dbb5e4fdf9bb60ae59de. which removed the path from the arn comparison.

Could you please kindly pull latest release and verify if it works for your scenario? If it doesn't, we can check this PR again.

Thank you!

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