Add init script for configuring datapusher

As discussed in #95, depends on this one to be
merged/pushed first:

ckan/ckan-docker-base#32

ckan/docker-entrypoint.d/01_setup_datapusher.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+if [[ $CKAN__PLUGINS == *"datapusher"* ]]; then
+   # Datapusher settings have been configured in the .env file
+   # Set API token if necessary
+   if [ -z "$CKAN__DATAPUSHER__API_TOKEN" ] ; then
+      echo "Set up ckan.datapusher.api_token in the CKAN config file"
+      ckan config-tool $CKAN_INI "ckan.datapusher.api_token=$(ckan -c $CKAN_INI user token add ckan_admin datapusher | tail -n 1 | tr -d '\t')"
+   fi
+else
+   echo "Not configuring DataPusher"
+fi