acp: Change default for gemini back to managed version (#45218)
Ben Brandt
created
It seems we unintentionally changed the default behavior of if we use
the gemini on the path in #40663
Changing this back so by default we use a managed version of the CLI so
we can better control min versions and the like, but still allow people
to override if they need to.
Release Notes:
- N/A