fix(Docker) Change container base image

[Vince-janv]

Description

It was discovered a while ago that the pythonXX-slim base images were not able to create worker threads (see this issue). This PR change the base image to python:3.8-slim-bullseye

Changed

• Base image change to python:3.8-slim-bullseye

Steps to consider while deploying

• Configuration changes:
• Documentation updates:
• Inform users by email:

Review:

• [ ] Code approved by
• [ ] Tests executed on stage by: (Document the test done with screen shots and description.)
• [ ] "Merge and deploy" approved by

This version is a:

• [ ] MAJOR - when you make incompatible API changes
• [ ] MINOR - when you add functionality in a backwards compatible manner
• [x] PATCH - when you make backwards compatible bug fixes or documentation/instructions

[Vince-janv]

Made change here instead for testing purposes