Use k6 release assets to build ov images

[dhruvkb]

Description

The k6 RPM only provides packages for the x86_64 architecture. Till the aarch version is not added to the RPM (grafana/k6#2136), we should use the assets from their GitHub Releases to get the platform specific build.

Additional context

This was brought up in issue #4931, and hot-fixed by #4932 to use Rosetta emulation. This is a more elegant solution that avoids emulation. The most ideal would however be for k6 to start providing aarch builds in their RPM.

[obulat]

I think most contributors will never use k6. Maybe building it should be optional?