Add DOCKER_STEPCA_INIT_PASSWORD_FILE variable for docker secrets

Add the management of the DOCKER_STEPCA_INIT_PASSWORD_FILE variable.  over DOCKER_STEPCA_INIT_PASSWORD.
If both are used only DOCKER_STEPCA_INIT_PASSWORD_FILE will be used.

docker/entrypoint.sh

@@ -46,7 +46,10 @@ function step_ca_init () {
         --provisioner-password-file "${STEPPATH}/provisioner_password"
         --address "${DOCKER_STEPCA_INIT_ADDRESS}"
     )
-    if [ -n "${DOCKER_STEPCA_INIT_PASSWORD}" ]; then
+    if [ -n "${DOCKER_STEPCA_INIT_PASSWORD_FILE}" ]; then
+        cat < "${DOCKER_STEPCA_INIT_PASSWORD_FILE}" > "${STEPPATH}/password"
+        cat < "${DOCKER_STEPCA_INIT_PASSWORD_FILE}" > "${STEPPATH}/provisioner_password"
+    elif [ -n "${DOCKER_STEPCA_INIT_PASSWORD}" ]; then
         echo "${DOCKER_STEPCA_INIT_PASSWORD}" > "${STEPPATH}/password"
         echo "${DOCKER_STEPCA_INIT_PASSWORD}" > "${STEPPATH}/provisioner_password"
     else