Implement custom scripts for mapstore

[f-necas]

Custom scripts

This PR adds the capability to run scripts at startup of the container.

It's a part of the georchestra PR :

• https://github.com/georchestra/georchestra/pull/4083

Soving issue :

• https://github.com/georchestra/georchestra/issues/4030

How-to

Set CUSTOM_SCRIPTS_DIRECTORY environment variable to point to a valid volume. Set a volume with scripts to execute.

Example :

 mapstore:
    image: georchestra/mapstore:latest
    ...
    volumes:
      - georchestra_datadir:/etc/georchestra
    environment:
      - CUSTOM_SCRIPTS_DIRECTORY=/etc/georchestra/mapstore/scripts