Create a simple HTTP service that exposes CLI functionality

[Lantero]

Currently, k6 Cloud services are written in Python, and this includes the script/archive validation engine.

This validation needs to check if extensions are being used and to what extent (Simple: use whatever version, Advanced: use specific versions). For advanced usage, more in particular, we need to verify if the user has the right subscription that would allow this.

It has been initially agreed that we start by running a subprocess of k6deps CLI and parsing its JSON response, but ideally we should expose an internal service, just like the builder or execution requirements, that can serve this purpose in a more efficient way.

This is not considered a priority/blocker, but a nice to have, at least initially, until we prove the subprocess approach is hurting our application in a meaningful way.