refactor: simplify and document config.ts (#238)

This PR cleans up the type definition for the configuration object, as well as commenting the hell out of it. There are no duplicate definitions, and I annotated what I could.

- `@optional` means providing a value isn't mandatory
- `@deprecated` means the field itself isn't necessary _anymore_ in `wrangler.toml`
- `@breaking` means the deprecation/optionality is a breaking change from wrangler 1
- `@todo` means there's more work to be done (with details attached)
- `@inherited` means the field is copied to all environments

I also added a stub for the validation function that will be applied to config objects. In the next PR, I will flesh that function out.

.changeset/good-rats-shave.md

@@ -0,0 +1,13 @@
+---
+"wrangler": patch
+---
+
+refactor: simplify and document `config.ts`
+
+This PR cleans up the type definition for the configuration object, as well as commenting the hell out of it. There are no duplicate definitions, and I annotated what I could.
+
+- `@optional` means providing a value isn't mandatory
+- `@deprecated` means the field itself isn't necessary anymore in wrangler.toml
+- `@breaking` means the deprecation/optionality is a breaking change from wrangler 1
+- `@todo` means there's more work to be done (with details attached)
+- `@inherited` means the field is copied to all environments