🚀 Feature: Watch mode with a configuration file

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Combining #35 and #36: I'd like to have watch mode support a local configuration file. That way you can preview what changes to your local repository will look like with different configs.

As in, if you run npx create --watch in a directory with a create.config.ts and then update create.config.ts, local file system changes will be re-applied.

Additional Info

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[JoshuaKGoldberg]

Merging back into #35 per #35 (comment). Since it'll be a lot of work, and #97 ended up needing to include config file support anyway, it's unclear to me how to split these issues up so far.