Fixed AWS 'teleport-generate-config' script when IMDSv2 is used

[fheinecke]

When using v2 of the EC2 metadata service to populate the /etc/teleport.yaml file requests fail due to an incorrectly formatted curl argument. This fixes the issue.

In Terraform parlance this occurs when the below is set on EC2 instance:

metadata_options {
   http_endpoint = "enabled"
   http_tokens   = "required"
}

Related issue: #10962