gitlab-ci: Update QEMU_JOB_AVOCADO and QEMU_CI_AVOCADO_TESTING

gitlab-ci: Update QEMU_JOB_AVOCADO and QEMU_CI_AVOCADO_TESTING

Since we don't run the Avocado jobs in the CI anymore, rename
these variables to QEMU_JOB_FUNCTIONAL and QEMU_CI_FUNCTIONAL.

Also, there was a mismatch between the documentation and the
implementation of QEMU_CI_AVOCADO_TESTING: While the documentation
said that you had to "Set this variable to have the tests using the
Avocado framework run automatically", you indeed needed to set it
to make the pipelines appear in your dashboard - but they were never
run automatically in forks and had to be triggered manually. Let's
improve this now: No need to hide these pipelines from the users
by default anymore (the functional tests should be stable enough
nowadays), and rather allow the users to run the pipelines auto-
matically with this switch now instead, as was documented.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250414113031.151105-15-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>