feat: add SSH host keys role

• Added SSH host keys role with tasks to ensure /tmp/ssh_keys directory, download host keys from S3, and unpack them to /etc/ssh.
• Configured ssh_host_keys_s3_bucket and ssh_host_keys_s3_object variables in group_vars/all to support S3 bucket and object information for SSH host keys.
• Added { name: 'ssh_host_keys', tags: 'ssh_host_keys' } entry in cheaha.yml to define the SSH host keys role.

ansible/group_vars/all

@@ -10,3 +10,12 @@
   nhc_download_path: "/tmp"
   nhc_git_repo: "https://gitlab.rc.uab.edu/rc/nhc.git"
   nhc_git_repo_path: "/tmp/nhc"
+
+#SSH Host Keys
+  s3_endpoint: ""
+  ssh_host_keys_s3_bucket: ""
+  ssh_host_keys_s3_object: ""
+
+# AWS credentials
+  lts_access_key: ""
+  lts_secret_key: ""