[ZEPPELIN-6358] Seperate environment config and shared utilities from #5101

[dididy]

What is this PR for?

In #5101, the amount of changes became too large, and a committer suggested splitting it into smaller parts. Since the updates related to the common test environment and shared utility functions have already proven to be stable, I separated those pieces into this dedicated PR.

This PR includes only the safe, standalone changes that improve the shared E2E environment and utilities.

[Summary of Changes]

• Refined and separated E2E test environment setup

  • Improved global setup/teardown

    • CI: using ZEPPELIN_E2E_TEST_NOTEBOOK_DIR
    • To use ZEPPELIN_E2E_TEST_NOTEBOOK_DIR locally, the server has to be restarted at least once, which feels a bit odd to enforce during E2E test execution. To make things less messy from a UI perspective, I reorganized the structure so that all tests are collected under E2E_TEST_FOLDER instead.

  • Added folder/notebook initialization and cleanup logic

    • you can run it standalone with this command:npm run e2e:cleanup(automatically run this once the tests are finished)

• Extracted shared utilities and constants

  • Added common E2E constant (e.g., E2E_TEST_FOLDER)
  • Introduced cleanup utilities to ensure stable post-test state

• Updated GitHub Actions (frontend.yml)

  • Added environment variables(for python interpreter), notebook repo initialization, and cleanup steps
  • Due to potential storage and cost concerns, I shortened the retention period for the Playwright report from 30 days to 3 days

• Updated Playwright / ESLint configurations

  • ts to cjs

What type of PR is it?

Improvement
Refactoring

Todos

What is the Jira issue?

ZEPPELIN-6358

How should this be tested?

cd zeppelin-web-angular
nvm use
npm run start
npm run e2e
npm run e2e:cleanup

Screenshots (if appropriate)

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[dididy]

I did some additional refactoring based on the previous PR(#5101) and reflected those changes here.
Git got slightly tangled, so commits ended up being squashed together, but aside from that, everything remains the same as before. The only actual change to review is in base-page.
Once this PR is merged, I’ll proceed with opening the remaining split PRs.
#5101 (comment)