docs: add more details to cloudflare workers bindings section

[jw-12138]

No description provided.

[yusukebe]

We don't recommend using Context for c for the following reasons:

https://hono.dev/docs/guides/best-practices#don-t-make-controllers-when-possible

[yusukebe]

The naming Env will be confusing because we often use the following code:

type Env = {
  Bindings: {
    KV: KVNamespace
  },
  Variables: {
    foo: string
  }
}

Actually, the code which is generated from C3 does not use Env but uses CloudflareBindings:

// Generated by Wrangler by running `wrangler types --env-interface CloudflareBindings`

interface CloudflareBindings {
	MY_VARIABLE: "production_value";
}