Adds iam:GetUser action for IAM Policy on AWS documentation

[ollaw]

Description

Updates AWS documentation to correct an omission in IAM permissions policy for Vault, more specifically the IAM Policy with boundary is missing the iam:GetUser action (which is present in the policy above without boundaries), which is also required to perform the root credentials rotation (vault write -f aws/config/rotate-root) when the root user configured starts with Vault, which is likely a common case for beginners.

TODO only if you're a HashiCorp employee

• Backport Labels: If this PR is in the ENT repo and needs to be backported, backport
  to N, N-1, and N-2, using the backport/ent/x.x.x+ent labels. If this PR is in the CE repo, you should only backport to N, using the backport/x.x.x label, not the enterprise labels.
  • If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
• Jira: If this change has an associated Jira, it's referenced either
  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
• ENT PR: If this change has an associated ENT PR, please link it in the
  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[hashicorp-cla-app]

All committers have signed the CLA.

[mpalmi]

@ollaw Apologies for the late feedback (after already approving), but would you mind dropping the changelog for this PR? Once you do that I'll go ahead and merge!

[ollaw]

@mpalmi no problem at all, is it fine this way or do I need to rebase?

[mpalmi]

@mpalmi no problem at all, is it fine this way or do I need to rebase?

We should be good to go. Thanks for the speedy reply.