Add support for a rhel9 based bastion

[manojnkumar]

Beta versions of rhel9 indicate that the preferred remote login over ssh is with a cloud-user id.
There could be other changes required to fully support a rhel9 based bastion/helper-node.

[yussufsh]

We need a sudo user access to configure bastion for OCP deployment without a password prompt.
If the concern is using a non-root user, we can now set it via the Terraform variable rhel_username.

Agree with complete test using RHEL9 to claim full support.

[yussufsh]

@manojnkumar I have tested Terraform SSH provisioner with v1.2.0 which worked with the CentOS 9 image given by @Shilpi-Das1.
So we need to just add it to the doc to use Terraform v1.2.0 or later for working with newer version of RHEL or CentOS.

[yussufsh]

Terraform v1.1.9:

│ Error: remote-exec provisioner error
│
│   with null_resource.bastion_init,
│   on main.tf line 10, in resource "null_resource" "bastion_init":
│   10:   provisioner "remote-exec" {
│
│ interrupted - last error: SSH authentication failed (root@<ip>:22): ssh: handshake failed:
│ ssh: unable to authenticate, attempted methods [none publickey], no supported methods remain

Terraform v1.2.0:

$ cat main.tf
resource "null_resource" "bastion_init" {
  connection {
    type        = "ssh"
    user        = "root"
    host        = "<ip>"
    private_key = file(coalesce("~/.ssh/id_rsa", "/dev/null"))
    agent       = false
    timeout     = "2m"
  }
  provisioner "remote-exec" {
    inline = [
      "whoami",
      "cat /etc/redhat-release"
    ]
  }
}
$ terraform apply -auto-approve

Terraform used the selected providers to generate the following execution plan. Resource actions are
indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # null_resource.bastion_init will be created
  + resource "null_resource" "bastion_init" {
      + id = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.
null_resource.bastion_init: Creating...
null_resource.bastion_init: Provisioning with 'remote-exec'...
null_resource.bastion_init (remote-exec): Connecting to remote host via SSH...
null_resource.bastion_init (remote-exec):   Host: <ip>
null_resource.bastion_init (remote-exec):   User: root
null_resource.bastion_init (remote-exec):   Password: false
null_resource.bastion_init (remote-exec):   Private key: true
null_resource.bastion_init (remote-exec):   Certificate: false
null_resource.bastion_init (remote-exec):   SSH Agent: false
null_resource.bastion_init (remote-exec):   Checking Host Key: false
null_resource.bastion_init (remote-exec):   Target Platform: unix
null_resource.bastion_init (remote-exec): Connected!
null_resource.bastion_init (remote-exec): root
null_resource.bastion_init (remote-exec): CentOS Stream release 9
null_resource.bastion_init: Creation complete after 4s [id=7421883950020013377]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

[yussufsh]

This one is resolved.