Optional. Defaults to latest. The version of the resource to
fetch.
If set to latest, scheduling will just find the latest available
version of a resource and use it, allowing versions to be skipped. This is
usually what you want, e.g. if someone pushes 100 git commits.
If set to every, builds will walk through all available versions of
the resource. Note that if passed is also configured, it will only
step through the versions satisfying the constraints.
If set to a specific version (e.g. {ref: abcdef123}), only that
version will be used. Note that the version must be available and detected by
the resource, otherwise the input will never be satisfied. You may want to
use check-resource to force detection of resource versions,
if you need to use an older one that was never detected (as all newly
configured resources start from the latest version).