add hooks to be able to launch a cmd after sucessfull upload

To be able to execute extra tasks after a content is uploaded, define a hooks section in the configuration file to be able to launch arbitrary commands

hooks:
  updated:
  - envlt -V MEILISEARCH=vault:myrole:kv/data/meilisearch#/data -- inject_secrets.sh file.json
  - envlt -V MEILISEARCH=vault:myrole:kv/data/meilisearch#/data -- /usr/bin/docs_scraper config.json