Support 'raw' bindings for bindings not directly supported by wrangler

[ObsidianMinor]

Rather than support every possible binding type (of which there are many, some internal), as a stop-gap we should support specifying an advanced "raw" bindings type that directly converts TOML into JSON as part of the metadata upload for a Worker. This would allow internal developers to use wrangler with bindings that aren't publicly available or are in internal beta.

[raw.internal]
type = "unsafe_internal_binding"
binding_field = "some value"

In the metadata.json, this would look like

{
    "name": "internal",
    "type": "unsafe_internal_binding",
    "binding_field": "some value"
},

It can be used to implement any existing binding as well, but note wrangler can't pick up on them and use them for instance in things like miniflare. As another example however, Service Bindings can be done as:

[raw.my_service]
type = "service"
service = "my_service"
environment = "production"

[Electroid]

This is important for "super secret" bindings that are either in development, or we have no intention of making public (for special internal features). We should do this.

[ObsidianMinor]

I can work on this provided we agree on a design.

[threepointone]

This looks great! We should do it with safeguards. Let's discuss on monday after I'm back? In particular, I'd like some warnings logged when someone uses these. I'd also like to understand what the behaviour is for some failure modes (for example, if service bindings were used in this manner but they don't work just yet in wrangler dev)

[ObsidianMinor]

For posterity here's the design agreed on:

• Add an unsafe table, currently with only a bindings sub-table. This can be expanded in the future to support uploading files or appending content to the script metadata of an upload.
• Keeping the design above, tables added to the bindings table will be appended to the bindings array in a worker upload.
  Example:

[[unsafe.bindings]]
name = "my_binding"
type = "unsafe_binding"

• These tables are only used during worker upload and edge previews, not during local previews. A warning will appear during local previews explaining this discrepancy.
• If a binding is written that has the same type as a binding handled by wrangler, a warning will also appear letting the user know that their binding as written isn't supported by wrangler and that they should migrate to a supported format for that binding.
  • For example, once Service Bindings go GA, if a user writes a service binding as

  [[unsafe.bindings]]
  name = "MY_SERVICE"
  type = "service"
  service = "my-service"
  environment = "production"

  They would receive a warning saying something along the lines of

  Raw 'service' bindings are not directly supported by wrangler. Consider migrating to a format for 'service' bindings that is supported by wrangler for optimal support. <insert link to doc>
  

  (wording can be changed)

[threepointone]

Fixed in #411, thank you very much @ObsidianMinor!