Use metadata server grouping as default

Metadata seems like a better way to group instances for autoscaling, so
switch metadata to be the default option. Note that stable/2024.2 and
older versions don't support metadata grouping, so the jobs are defined
to use prefix grouping instead.

Change-Id: Id1c62255e58e9ceeffad2512a3e8e083c3d13f8b
2 files changed