YAML: `group` should also accept a key `actions:` like the Python API

Description

Especially given the lack of documentation, children: in the YAML frontend is an opaque implementation detail. The Python API takes Group(actions=...) so I believe so should YAML.

Motivation

More intuitive usage for YAML

Design / Implementation Considerations

The children: special key is an implementation detail that is not present in XML because of its structure.

<group if="condition">
  <child />
</group>

In YAML the various lists of items that would go into the XML tag body are instead implemented as keys. The catch-all key is children:

group:
  if: condition
  children:
    - child:

In some other cases the children may be heterogenous attribute lists instead of Actions, so those are always implemented with an explicit name,

<node>
  <param name="x" value="y" />
</node>

- node:
    param:
      - name: x
        value: y

I think it's fine to continue to have children: as the fallback, especially to not break existing usage, but adding an additional option for actions: to match the Python API makes a lot of sense. This would apply to any other Actions that take child actions (as noted, attributes must always be explicitly named so that's not a problem), if there are any

Additional Information

No response