[feat] FlowPath - add conditional logic to be able to move to next step

[jstukas]

In a flow, we have a call out to an external system. While that is running there is a spinner over the fields of the component, but the buttons (Next most significantly) are available to users. If they click next, the flow stops in error. While we can error trapping logic, it would be a better user experience to hide the standard footer and only allow users to move forward once we have a successful reply from the external system.

This could also be based on other conditions of course (only activate a Next button once all required info is entered, for example).

This is currently on Flow roadmap, but > 1 year out, or else this solution looks like it could handle the requirement, https://unofficialsf.com/flow-button-bar-new-and-improved/

[pegros]

@jstukas actually the issue is not on this component but on the other one.
this componet should implement the validate() API method (see https://developer.salesforce.com/docs/component-library/documentation/en/lwc/lwc.use_flow_validate_user_input_for_custom_components) to prevent the "next" operation to actually execute.
I may demo a simple implementation for tests if necessary.