Using local debian repo: Speed up the image building.

Summary

Using the local package repositories.

Focus

Is such a hard coded repository acceptable?

Test Environment

Look at pipeline job: https://gitlab.indiscale.com/caosdb/src/caosdb-pylib/-/jobs/135250

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related issues #142 (closed)
• Up-to-date CHANGELOG.md (or not necessary)
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

unittests/docker/Dockerfile

 FROM debian:latest
+# Use local package repository
+COPY sources.list.local /etc/apt/
+RUN mv /etc/apt/sources.list /etc/apt/sources.list.orig
+RUN cat /etc/apt/sources.list.local /etc/apt/sources.list.orig > /etc/apt/sources.list
 RUN apt-get update && \
     apt-get install -y \
       pylint3 python3-pip tox git \