Do not parse full config for commands that don't need it

[unstubbable]

Motivation

The cleanup job for the Feature Hub (using the purge command) currently fails with the following Zod validation error:

[
  {
    "code": "too_small",
    "minimum": 1,
    "type": "array",
    "inclusive": true,
    "exact": false,
    "message": "Array must contain at least 1 element(s)",
    "path": [
      "routes"
    ]
  }
]

This is because the routes are inferred from the built documentation. But when running the purge command, we don't actually need the routes, and we also don't want to build the docs just to avoid the config validation error.

Proposed Solution

For a couple of commands (including purge) we only need the domain name parts (hostedZoneName and sometimes aliasRecordName), so we can limit the parsing/validation to those fields, and thus implicitly allow an empty array of routes in this context.

[unstubbable]

I would also be fine with merging the three files read-stack-config.ts, parse-stack-config.ts, and parse-domain-name-parts.ts into a single file called stack-config.ts. Or do you prefer it to be separated?

[clebert]

I would also be fine with merging the three files read-stack-config.ts, parse-stack-config.ts, and parse-domain-name-parts.ts into a single file called stack-config.ts. Or do you prefer it to be separated?

I don't really like the ergonomics of the functions, they are very fragmented and therefore unintuitive to use, but right now I don't have a better suggestion either. But one function per file is usually my preferred structure, so it fits.