ci: build with xk6 docker image in addition to local xk6

[roobre]

Description

A locally-installed xk6 build might succeed while a build for the same working tree might fail if run from a docker container. I suspect the reason for this might be that the grafana/xk6 container is using go 1.20, while locally we are building with 1.19.

As building with docker is the recommended approach in the xk6 repo, this PR adds a step to the CI to try building k6+disruptor with xk6 in docker.

Related: #330

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make test) and all tests pass.
• I have run relevant integration test locally (make integration-xxx for affected packages)
• I have run relevant e2e test locally (make e2e-xxx for disruptors, or cluster related changes)
• Any dependent changes have been merged and published in downstream modules
  

[pablochacin]

As building with docker is the recommended approach in the xk6 repo

However, the recommended way to build the disruptor is using the locally installed xk6. If we are changing the way the ci works, we should update the documentation

[roobre]

I think it's fine to keep our current recommended way and docs, unless we have reasons to change them. This PR merely adds another check for an alternative build path we've seen other people use in the wild (probably by recommendation of the xk6 repo).