Add ClickHouse CT template and installer

Introduce ClickHouse support by adding a container template (ct/clickhouse.sh), an installer script (install/clickhouse-install.sh) and app metadata (json/clickhouse.json). The installer configures ClickHouse to listen on 0.0.0.0, restarts the service, and performs OS update, networking checks, MOTD/customization and cleanup. Metadata declares default resources (2 CPU, 4GB RAM, 10GB disk), interface port 8123, documentation/website links, and a warning about the default user having no password.

install/clickhouse-install.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+# Copyright (c) 2021-2026 community-scripts ORG
+# Author: community-scripts ORG
+# License: MIT | https://github.com/community-scripts/ProxmoxVED/raw/main/LICENSE
+# Source: https://clickhouse.com
+
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+color
+verb_ip6
+catch_errors
+setting_up_container
+network_check
+update_os
+
+setup_clickhouse
+
+msg_info "Configuring ClickHouse"
+cat <<EOF >/etc/clickhouse-server/config.d/listen.xml
+<clickhouse>
+    <listen_host>0.0.0.0</listen_host>
+</clickhouse>
+EOF
+systemctl restart clickhouse-server
+msg_ok "Configured ClickHouse"
+
+motd_ssh
+customize
+cleanup_lxc