Add app client into framework

I've noticed in practice, configurators implementations have a large amount of adhoc API calls. It'd be nice to have a client abstraction to cleanly model this in one place, and have better ergonomics (ie, have a simple re-usable retryable get and some sugar).

I'm sure there's a similar challenge with static files in prestart configurators, but I haven't looked into that.

The more structure we can bring to configurators (so folks dont need to do adhoc curl/api requests in the happy path), the easier it will be for app contributions that are reliable.

No files, tests, or entry points are named. Start by locating the configurator framework and its existing ad hoc API calls, then clarify the client abstraction and retry behavior with maintainers. Done means configurators can use an agreed reusable client instead of repeated direct API requests.

Written by the indexing model from the issue text.