[Solr] Initialize datasets in solr when starting shanoir

[jcomedouteau]

• Add an automatic indexation when starting Shanoir
• Add an environnement variable to define this logic
• Add dependence in docker-compose / entrypoint so that solr starts before datasets

[a-ba]

I would even push for a fully-automated solution :

• have the solr container detect at startup that the configuration was changed and then wipe the data dir with something like:

  CMD ["/bin/sh", "-c", "
  (
      set -e
      cd /etc/shanoir-core-template
      for file in `find -type f` ; do
          cmp -- "$file" "/var/solr/data/shanoir/$file"
      done
  ) || (
      echo 'deleting /var/solr/data (not up-to-date with the template), the index has to be rebuilt'
      rm -rf /var/solr/data 
  )
  exec solr-precreate shanoir /etc/shanoir-core-template
  "]

• have the datasets container make a solr query on at startup and trigger the indexing task if it detects that the index is empty.