cmd: replace SetContext + Execute with ExecuteContext

[roobre]

Description

This PR removes the only usage of SetContext in cobra.Command instances. This will unblock downgrading cobra to 1.4.x, which is the same version k6 is using upstream.

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]

LGTM