Enhance Dockerfile and entrypoint script for Kerberos initialization

- Added krb5-admin-server and updated entrypoint to ensure proper initialization of the Kerberos realm.
- Improved error handling for required environment variables in entrypoint script.
- Updated README with additional prerequisites and client configuration instructions.
- Modified env.example to remove default passwords for security.
- Enhanced run-container script to set container hostname based on KDC_HOST.

scripts/run-container.sh

@@ -3,8 +3,16 @@
 set -e
 
 if command -v container >/dev/null 2>&1; then
+    ENV_FILE=~/app-data/kerberos/kerberos.env
+    KDC_HOST=$(grep -E '^KRB5_KDC_HOST=' "${ENV_FILE}" | cut -d= -f2-)
+    if [ -z "${KDC_HOST}" ]; then
+        echo "Error: KRB5_KDC_HOST is not set in ${ENV_FILE}" >&2
+        exit 1
+    fi
+
     container run -d --name kerberos \
-        --env-file ~/app-data/kerberos/kerberos.env \
+        --hostname "${KDC_HOST}" \
+        --env-file "${ENV_FILE}" \
         -v kerberos_data:/var/lib/krb5kdc \
         -p 88:88/tcp -p 88:88/udp \
         -p 464:464/tcp -p 464:464/udp \