[Preview] Add support for skew protection

[vicb]

There are 2 main files in this PR:

packages/cloudflare/src/cli/commands/skew-protection.ts (build time)

This builds a mapping from deploymentId to the worker version at build time.
Note that because the worker you are building has no version yet, "current" is used instead.

packages/cloudflare/src/cli/templates/skew-protection.ts (runtime)

At runtime, if a particular version is requested and it is present in the mapping,
we'll fetch the result from a preview URL with a hostname of <version>-<worker_name>.<domain>.workers.dev

How to use it:

• set cloudflare.skewProtectionEnabled to true in your OpenNext config
• provide values for the new env vars added to packages/cloudflare/src/api/cloudflare-context.ts
• update your next config to set the deployementId - you can use the getDeploymentId() helper

TODO:

• add tests
• handle assets (will need to run the worker before the asset worker)
• follow-up: move the skew protection logic in the aws/routing layer with pluggable overrides

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Latest commit: b373c64

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commit: b373c64

[conico974]

I just took a really quick look for now, will make a proper review later

[conico974]

I don't think this one will work if people uses durable object, for these cases you could use Cloudflare-Workers-Version-Overrides headers with the worker binding.

[vicb]

Cloudflare-Workers-Version-Overrides can only access one of 2 versions in a gradual deployment :(

[james-elicx]

I think this is looking pretty good on my initial read though. Going to have another look later on as well.