ci, valve: Add support scripts for the Valve bare-metal farm.

ci, valve: Add support scripts for the Valve bare-metal farm.

- Add the scripts to the prepared Mesa artifacts for use in later
runner stages.

- Add a template generator (generate_b2c.py) which reads and
validates (very lightly for now) the Gitlab job environment and then
spits out a YAML file describing the necessary test workload to be
sent to a Valve CI gateway.

Acked-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Martin Roukala <martin.roukala@mupuf.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14660>