feat!: add Remix, make dev port optional

[jlengstorf]

This starts the process of adding Remix to framework detection. There are a few open questions that I think I need @netlify/integrations to help with:

1. Right now we have to run both remix watch and netlify dev together and I'm not sure how to approach that or if it's possible to simplify
2. Remix uses port 8888, which I think is going to cause problems and I'm not sure if there's config available to fix it

I'm happy to close this PR if you've already got one rolling. If not, I figured I'd try to get the ball rolling as much as possible so we can get seamless Remix support in place.

Thanks!

[erezrokah]

@ascorbic, assuming we do netlify/cli#3655 (only run the dev command and use a static server), this should work for Remix correct? If so can you approve it?

Putting aside the CLI server port, which we can handle in another issue.

[ascorbic]

Yes, but critically important that this isn't released without that, as it will break all Remix builds otherwise.

[ascorbic]

But don't release until the CLI can handle it!

[erezrokah]

But don't release until the CLI can handle it!

Going to release under a major version (as it's a breaking change), then handle the CLI renovate PR manually.