add support for configuring root authorized_keys file

start.sh

@@ -2,6 +2,12 @@
 
 mkdir -p /run/sshd
 
-chown root: /root/.ssh/authorized_keys
+if [ -n "$ROOT_AUTHORIZED_KEYS" ]; then
+    if [ -f "$ROOT_AUTHORIZED_KEYS" ]; then
+        mkdir -p /root/.ssh
+        cp "$ROOT_AUTHORIZED_KEYS" /root/.ssh/authorized_keys
+        chmod 600 /root/.ssh/authorized_keys
+    fi
+fi
 
 exec /usr/sbin/sshd -D -e