Add Glicid long logo and update CI config

• Add Glicid logo with long svg version:

• Move logo to top left:

• Improve context image layout on small screen:

• Deploy to Gitlab Pages except on main and add environnement names and urls:

pages:
  ...
  except:
      - main
   ...
  environment:
    name: Staging env
    url: https://glicid.univ-nantes.io/doc/site_institutionnel/

deploy on guix:
  ...
  only:
    - main
  ...
  environment:
    name: Prod env
    url: https://glicid.fr