fix: use declared variable for client private key destination

The task importing the client private key referenced
`certificate_authority_client_ca_path`, a variable that is declared neither in
`defaults/main.yaml` nor in `meta/argument_specs.yaml`. Every run with
`certificate_authority_client_create: false` therefore aborted with an undefined
variable error before the key was written. Use the actual role variable
`certificate_authority_client_path` instead.

Co-authored-by: Copilot <copilot@github.com>

tasks/client_certificate_import.yaml

@@ -3,7 +3,7 @@
 - name: Import private key of a client
   ansible.builtin.copy:
     content: "{{ certificate_authority_client_tls_key_content }}"
-    dest: "{{ certificate_authority_client_ca_path }}/privkey.pem"
+    dest: "{{ certificate_authority_client_path }}/privkey.pem"
     owner: "root"
     group: "root"
     mode: "0600"