CI: Generate ssh key pair on the fly

There is litte reason to share an ssh key common to all CI jobs, so
generate one for each on the fly.

Also use plain-text cloud-init config instead of base64 for readability

tests/cloud_playbooks/roles/packet-ci/tasks/main.yml

@@ -3,6 +3,13 @@
   include_vars: "../files/{{ ci_job_name }}.yml"
   when: molecule_yml is not defined
 
+- name: Generate SSH keypair
+  community.crypto.openssh_keypair:
+    size: 2048
+    path: "{{ lookup('env', 'ANSIBLE_PRIVATE_KEY_FILE') }}"
+    mode: '400'
+  register: ssh_key
+
 - name: Start vms for CI job
   kubernetes.core.k8s:
     definition: "{{ lookup('template', 'vm.yml.j2', template_vars=item) }}"