Add permanent storage for Dolibarr documents Template

[giodc]

i have tried the dolibarr Template, and the storage for Documents, is not set. based on my test, if the container is restarted - rebuilded, the documents uploaded disappear.

i have made a test and i believe that this is sufficent to map a permanent storage under the dolibarr service:

volumes:
  - 'dolibarr_documents_data:/var/www/documents/'

not sure 100% if is ok! it may be a great features, thanks!