Update tutor-mfe to use Node 20

[arbrandes]

Description

See https://github.com/openedx/public-engineering/issues/267 for the general motivation and mechanism.

Once all officially supported Tutor MFEs have flipped over to use Node 20 (after step 3 as described above), start building the MFE image using Node 20.

Node 20 status per MFE

• [x] frontend-app-authn
• [x] frontend-app-account
• [x] frontend-app-communications
• [x] frontend-app-course-authoring
• [x] frontend-app-discussions
• [x] frontend-app-ecommerce
• [x] frontend-app-gradebook
• [x] frontend-app-learner-dashboard
• [x] frontend-app-learner-record
• [x] frontend-app-learning
• [x] frontend-app-ora-grading
• [x] frontend-app-payment
• [x] frontend-app-profile

(The list above will get updated with the relevant PRs to make it easier to see when we can proceed, here.)