feat: allows you to add extra pip requirements to your codejail sandbox DS-697

[MaferMazu]

Description

This PR allows you to add extra pip requirements to your codejail sandbox.

Related: #41

How to test

1. Install this version of tutor-contrib-codejail.
2. Add in your tutor config.yml the following:

CODEJAIL_EXTRA_PIP_REQUIREMENTS:
- pybryt

(You can use any pip package)
3. Save your configuration in Tutor.

tutor config save

4. Create a new codejail image.

tutor images build codejail

5. Run codejail.

tutor local do init --limit codejail

6. Launch your environment.

tutor local launch

Expected Behavior

• You should be able to import the package you installed in a loncapa problem.
  (In Studio > Create a course > Create a Subsection > Create a Unit > Add a Problem > Select Advance and Custom Python-Evaluated Input > Edit the problem > Import the package you installed in the loncapa script)
  Example:

<script type="loncapa/python">
import pybryt

def test_add_to_ten(expect, ans):
    return test_add(10, ans)

</script>

[bra-i-am]

Working as expected!

[luisfelipec95]

looks good to me