Improve DockerHub image with "slim" image

The following discussion from !5 (merged) should be addressed:

• @dzc34 started a discussion:

  Peut-être utiliser une image slim

  • openjdk:8u312-jre-bullseye --> 273 MB + Asqatasun = 800 MB
  • openjdk:8-jre-slim-bullseye --> 194 MB + Asqatasun = 684 MB