feat: migrate SSL configuration to centralized https.conf snippet

snippets/https.conf.template

@@ -0,0 +1,5 @@
+listen 443 ssl;
+listen [::]:443 ssl;
+
+ssl_certificate /etc/nginx/certs/${BASE_DOMAIN}/fullchain.pem;
+ssl_certificate_key /etc/nginx/certs/${BASE_DOMAIN}/key.pem;