This change adds a flag on providers that allows users to disable JIT
configuration even when it's available. For context, JIT is available
on github.com and any GHES instance >=3.10.
This option is a stopgap measure for providers that have not yet been
updated to use JIT configs instead of runner registration tokens.
Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>