"cci task run create_package_version" should allow option "version_base: default" in cumulusci.yml

[RupertBarrow]

Feature Type

I'm interested in functionality that solves a current problem or limitation in how CumulusCI works.

Does your feature request solve a current problem?

Currently, the release_unlocked_beta flow sets option create_package_version__version_base to latest_github_release by default in CCI's code https://github.com/SFDO-Tooling/CumulusCI/blob/6368154b2443db93ae6787a491492e5c6b23ceaa/cumulusci/cumulusci.yml#L1173.

If I want to customize this behaviour to restore the default behaviour to "create_package_version__version_base = the highest existing version number of this package", there is no available syntax to do that.

Describe the solution you'd like

One should be able to reset that option to default by something like "create_package_version__version_base default" or ""create_package_version__version_base highest"

Describe alternatives you've considered

There are none, other than cloning the whole definition of the release_unlocked_beta flow into a custom flow in which create_package_version__version_base would simply not be set

Additional context

No response

[yippie]

I agree this type of change is an issue. Some tasks the only way to specify a specific behavior is to specify nothing/null value for the parameter. However, CumulusCI has no way to override a value with a null/unset.

In general, we need 1 of 2 solutions (or both!)

1. Add support for "unset" overrides when overriding task parameters via CLI options or via flow overrides.
2. Require?/Add explicit values for ALL behavior options. Null for an attribute should set a default value, not EVER be a value in and of itself. There should always be an explicit value available to get the same behavior as not specifying the attribute.