feat: Codegen v2

[alexluong]

This is a WIP PR with a good POC for the new codegen.

It supported the pattern where you can use do this

resource "hookdeck_destination" "destination" {
  name = "destination"
}

resource "hookdeck_connection" "connection_shopify" {
  name           = "connection_shopify"
  destination_id = hookdeck_destination.destination.id
  source_id      = hookdeck_shopify_source.source_shopify.id
}

resource "hookdeck_shopify_source" "source_shopify" {
  name = "source_shopify"
}

resource "hookdeck_shopify_source_config" "shopify_config" {
  source_id = hookdeck_shopify_source.source_shopify.id
  auth = {
    webhook_secret_key = "example-secret-key"
  }
}

Currently, the hookdeck_shopify_source doesn't support setting its own config yet, but that's doable next.

Please check this out and QA to see if things make sense!

Next steps:

• support hookdeck_shopify_source.config
• support data source (can be a next version)
• generate source from OpenAPI instead of hard-coded template (probably should be a follow-up)

Not a blocker but @alvarp mentioned there will be some changes to the source response which can help with the code, so I'm waiting for that. For now, I was able to get things to work with some hacky code, so not a blocker for now.