Add CI workflow that runs only changed E2E tests, and succeeds when no tests have changed

[tpaksu]

Context: p1737719556299039-slack-C01B8KNUYSW

Changes proposed in this Pull Request

Testing instructions

This PR adds a workflow that runs only the modified E2E tests in it, helping us see the errors faster (~5-10 minutes) without waiting for all tests to complete (Which takes around 35-40 minutes to complete now, before optimizations). Also updates Playwright to 1.50, since the --only-changed option was added in v1.46, and we were using v1.43.

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• Run npm run changelog to add a changelog file, choose patch to leave it empty if the change is not significant. You can add multiple changelog files in one PR by running this command a few times.
• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Post merge

• Link to testing instructions from release testing doc following these instructions : Add link here / 'QA Testing Not Applicable'
• Add or update critical flows and testing instructions for critical flows, if applicable.
• Add what's changed (description, screenshot, demo videos etc.) to the release announcement post, if applicable.