Figure out a way to include an external manifest as base dependencies (defaults)

[Lantero]

In k6 Cloud, we are defining a base manifest for any given k6 release (A concept that encapsulates a given set of k6 versions and extensions to a subset of customers). This base manifest serves as a list of defaults that can be overriden by the pragma definitions that the user might put in their k6 scripts.

Whilst this works for anything that is orchestrated in the cloud (UI tests which archive and execute both in the cloud) or CLI tests (Execution phase), it does not cover the case where k6exec is involved: k6 Cloud archive phase of CLI tests.

This means that k6exec does not have access to this manifest and can only build the binary for archiving based on the cloud catalog and the pragmas.

Relates to (and likely depends on) grafana/k6deps#63