Use k6foundry for building

[pablochacin]

Replace build logic with k6foundry library. Also, refactors the build argument parsing logic to facilitate testing.

This change required upgrading to golang 1.22 (required by k6foundry).

Breaking change in xk6.Build library: the Build method no longer completes missing attributes using environment variables. The function FromOSEnv can be used to create Builder from the environment variable and then override or complete its attributes. See README.md for an example

Fixes #112

[szkiba]

The exit code on error should be fixed (it should be 1 as before). Probably a lot of automation depends on this.

There is a problem with building private extensions. The following should work (it worked with the old xk6), but it doesn't:

export GOPRIVATE=github.com/grafana/hackathon-2024-12-weaver-spiders
xk6 build --with github.com/grafana/hackathon-2024-12-weaver-spiders 

[szkiba]

LGTM