gitlab: support disabling job auto-run in upstream

gitlab: support disabling job auto-run in upstream

In forks QEMU_CI=1 can be used to create a pipeline but not auto-run any
jobs. In upstream jobs always auto-run, which is equiv of QEMU_CI=2.

This supports setting QEMU_CI=1 in upstream, to disable job auto-run.
This can be used to preserve CI minutes if repushing a branch to staging
with a specific fix that only needs testing in limited scenarios.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230608164018.2520330-6-berrange@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>