[cli] Add tests to compare dev/prd image optimization

[styfle]

Add E2E test for to test image optimization against vc dev as well as a prod deployment.

📋 Checklist

Tests

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR (CH13104)

[juancampa]

@styfle does vc dev return last-modified? That's something that people have asked about, imgix returns it and we simply forward it

[styfle]

@juancampa No it does not. The next dev implementation uses etag instead (per @Timer) which is why it was omitted from these tests. See vercel/next.js#18986

[juancampa]

Got it, that's an inconsistency that we might want to fix later

[Timer]

@juancampa I think the inconsistency is inherent to the fact that Next.js is optimizing the image itself (thus has the Etag readily at its disposal) verses on Vercel where we proxy Imgix. I don't see the need to be consistent here.

[juancampa]

I could see users being confused by etags appearing in their vc dev experience, but not in prod. But yeah, for now I think it's okay to accept that there are some (non fundamental) differences between the two environments

[TooTallNate]

Why is this necessary?

[styfle]

Its not necessary but it will help us catch differences in @vercel/next canary before they go to stable