ci: Use workflow to make CI aware of performance jobs

ci: Use workflow to make CI aware of performance jobs

With the workflow keyword, we can have more control over how pipelines
are created.

One of the features is to set a variable for the entire pipeline
depending on the rule. These variables would be available for all jobs
manifest and can be used inside job rules, for example.

We can use that to set a variable to enable performance jobs in the
pipeline, both at the YAML and script levels.

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21492>