Jupyterhub update to dev

[filippomc]

Closes CH-110
Closes CH-94

Implemented solution for CH-110: jupyterhub helm chart updated to the latest from https://github.com/jupyterhub/zero-to-jupyterhub-k8s/tree/main -- 3.2.1. The procedure to update has been documented and scripted.
Implemented solution for CH-94: A dedicated field has been added to harness.jupyterhub so that the images to be prepulled can be configured.

How to test this PR: Run a deployment with jupyterhub like harness-deployment . -i jupyterhub -d ch -dtls -e test-local -n ch -u -t latest and then open http://hub.ch

Compartibility notes

Jupyterhub images must be changed to derivate from quay.io/jupyterhub/k8s-hub:3.2.1

Sanity checks:

• The pull request is explicitly linked to the relevant issue(s)
• The issue is well described: clearly states the problem and the general proposed solution(s)
• From the issue and the current PR it is explicitly stated how to test the current change
• The labels in the issue set the scope and the type of issue (bug, feature, etc.)
• All the automated test checks are passing
• All the linked issues are included in one milestone
• All the linked issues are in the Review/QA column in Jira
• All the linked issues are assigned

Breaking changes (select one):

• The present changes do not change the preexisting api in any way
• This PR and the issue are tagged as a breaking-change

Possible deployment updates issues (select one):

• There is no reason why deployments based on CloudHarness may break after the current update
• This PR and the issue are tagged as alert:deployment

Test coverage (select one):

• Tests for the relevant cases are included in this pr -- added e2e somke test
• The changes included in this pr are out of the current test coverage scope

Documentation (select one):

• The documentation has been updated to match the current changes
• The changes included in this PR are out of the current documentation scope