Improve deployment documentation

This is the part 1 of https://redmine.teklia.com/issues/8008

• List of S3 buckets to create & why they are needed
  • explain how to create these through mc alias + mc mb
• Add smtp+tls account into requirements
• replace docker run by docker exec on first run
• Add a section on setup for postgres to:
  1. create a nonsuperuser user for arkindex backend
  2. create extensions through admin on the arkindex db:
     • hstore
     • btree_gist
• Document arkindex admin existence !
  • user creation
  • corpus MGMT
  • RQ worker dedicated pages