Remove JUPYTER_IMAGE env variable from Notebook CR

[atheo89]

Related to: https://issues.redhat.com/browse/RHOAIENG-7551

Description

As the JUPYTER_IMAGE env variable is not used, we can clean up our code

How Has This Been Tested?

Should be tested in conjunction with dashboard PR changes:

1. Modify rhoai-operator DSC .yaml with devFlags that correspond to workbench changes

    workbenches:
      devFlags:
        manifests:
          - contextDir: components/odh-notebook-controller/config
            uri: 'https://github.com/atheo89/kubeflow/tarball/RHOAIENG-7551'
      managementState: Managed

2. Modify rhods-dashboard deployment to use quay.io/opendatahub/odh-dashboard:pr-3407 image

3. Deploy a workbench on RHOAI. Run the following command env | grep JUPYTER_IMAGE on workbench's terminal to ensure that the JUPYTER_IMAGE environment variable is not present. As well as should check on the Notebook CR that there is no env.JUPYTER_IMAGE.

4. Drop the internal registry and re-run step 3.
   oc edit configs.imageregistry.operator.openshift.io -n openshift-image-registry change spec.ManagmentState to Removed

5. Inspect the odh-notebook-controller deployment logs for suspicious entries related to JUPYTER_IMAGE. Check the logs of the odh-notebook-controller deployment. Ensure that there are no logs/errors mentioning JUPYTER_IMAGE.

Merge criteria:

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[openshift-ci]

Skipping CI for Draft Pull Request.
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You can still manually trigger a test run with /test all

[openshift-ci]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.12%. Comparing base (330d816) to head (24ab7a7).

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #505       +/-   ##
===========================================
+ Coverage   55.27%   71.12%   +15.85%     
===========================================
  Files           9        7        -2     
  Lines        2276     1330      -946     
===========================================
- Hits         1258      946      -312     
+ Misses        922      319      -603     
+ Partials       96       65       -31     

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[atheo89]

The discussion of this env removal is under discussion JFR: https://redhat-internal.slack.com/archives/C060A5FJEAD/p1736866386274129

[atheo89]

Related with dashboard PR: opendatahub-io/odh-dashboard#3407

[atheo89]

After discussing with the team, we have decided not to proceed with removing the JUPYTER_IMAGE environment variable from the notebook CR, as it is currently used in our QE tests on the ODS-CI test platform.
We will revisit the possibility of its removal once we transition away from this dependency.
I am closing this PR for now.