Standardize database naming in Docker env config

Updated the DATABASE_URL environment variable to dynamically use the
specific `linkwarden_name` value rather than a hardcoded database name.

roles/linkwarden/defaults/main.yml

@@ -78,7 +78,7 @@ linkwarden_docker_envs_default:
   STORAGE_FOLDER: "/data"
   NEXTAUTH_SECRET: "{{ linkwarden_secret_key.stdout }}"
   NEXTAUTH_URL: "{{ linkwarden_web_url }}/api/v1/auth"
-  DATABASE_URL: "postgresql://{{ user_name }}:{{ postgres_docker_env_password }}@{{ linkwarden_name }}-postgres:5432/saltbox"
+  DATABASE_URL: "postgresql://{{ user_name }}:{{ postgres_docker_env_password }}@{{ linkwarden_name }}-postgres:5432/{{ linkwarden_name }}"
 linkwarden_docker_envs_custom: {}
 linkwarden_docker_envs: "{{ linkwarden_docker_envs_default
                             | combine(linkwarden_docker_envs_custom) }}"