Simplify init scripts

Single script init.sh which performs the following tasks:
- Creates required directory structure
- Activates python venv (if required)
- Waits for database connection
- Runs command

docker/init.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+# exit when any command fails
+set -e
+
+# Create required directory structure (if it does not already exist)
+if [[ ! -d "$INVENTREE_STATIC_ROOT" ]]; then
+    echo "Creating directory $INVENTREE_STATIC_ROOT"
+    mkdir -p $INVENTREE_STATIC_ROOT
+fi
+
+if [[ ! -d "$INVENTREE_MEDIA_ROOT" ]]; then
+    echo "Creating directory $INVENTREE_MEDIA_ROOT"
+    mkdir -p $INVENTREE_MEDIA_ROOT
+fi
+
+# Check if "config.yaml" has been copied into the correct location
+if test -f "$INVENTREE_CONFIG_FILE"; then
+    echo "$INVENTREE_CONFIG_FILE exists - skipping"
+else
+    echo "Copying config file to $INVENTREE_CONFIG_FILE"
+    cp $INVENTREE_HOME/InvenTree/config_template.yaml $INVENTREE_CONFIG_FILE
+fi
+
+# Setup a python virtual environment
+# This should be done on the *mounted* filesystem,
+# so that the installed modules persist!
+if [[ -n "$INVENTREE_PY_ENV" ]]; then
+    echo "Using Python virtual environment: ${INVENTREE_PY_ENV}"
+    # Setup a virtual environment (within the "dev" directory)
+    python3 -m venv ${INVENTREE_PY_ENV}
+
+    # Activate the virtual environment
+    source ${INVENTREE_PY_ENV}/bin/activate
+
+    # Note: Python packages will have to be installed on first run
+    # e.g docker-compose -f docker-compose.dev.yml run inventree-dev-server invoke install
+fi
+
+# Wait for the InvenTree database to be ready
+# cd ${INVENTREE_MNG_DIR}
+# echo "InvenTree: Waiting for database connection"
+# invoke wait && echo "InvenTree: Database connection successful" || { echo "InvenTree: Failed to connect to db due to errors, aborting"; exit 1; }
+# sleep 5
+
+cd ${INVENTREE_HOME}
+
+# We assume at this stage that the database is up and running
+# echo "InvenTree: Checking database..."
+# invoke check || exit 1
+
+# Can be run as a cron job or directly to clean out expired sessions.
+# cd ${INVENTREE_MNG_DIR}
+# python3 manage.py clearsessions || exit 1
+
+# Launch the CMD *after* the ENTRYPOINT completes
+exec "$@"