refactor: improve project structure, idempotency, and security

- Replace interactive python setup script with native Ansible vars_prompt.

- Add missing Prometheus helm values template for resource management on Raspberry Pi.

- Replace deprecated apt_key module usage with modern keyring file download.

- Add project files: requirements.txt, requirements.yml, and .gitignore.

requirements.yml

@@ -0,0 +1,6 @@
+# External Ansible dependencies
+# Install using: ansible-galaxy install -r requirements.yml (for roles)
+# and: ansible-galaxy collection install -r requirements.yml (for collections)
+
+collections:
+  - name: kubernetes.core