Update IAM policy template

[eduardoweiland]

This should be the same as #32 but using the same policy template from upstream fix: kubernetes-sigs/aws-load-balancer-controller#3046. It's a more restrict version of the policy in #32.

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[anphlax]

This PR is highly needed. I was about to open a similar one, but found that this is the correct solution to the issue that creating targetGroups is not possible, due to wrong IAM Conditional Policy Statements.

[anphlax]

Please consider merging it soon, this TF module is the most used according to the terraform registry stats.

[brunodasilvalenga]

LGTM

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