Add license change event

[mjherzog]

A license change is a major event in the lifecycle of a component which often has a significant impact on whether an organization can/will continue to use the component.

This is a request to add 'licenseChange' as a new Event type.

A draft description is:
Category: Version Event
The manufacturer or maintainer makes a major change to the license for a component or service. The license change usually applies to a new component version and is not retroactively applied to prior versions.

This license change is intended to capture changes in licenses that are published to the public and not the license terms negotiated directly between a supplier and customer. The license may be open source or proprietary or somewhere in-between.

[ljharb]

Hopefully it would be paired with a major version release (assuming semver), since changing a license is a breaking change.

We should definitely add this.

[mjherzog]

In our experience (AboutCode/ScanCode) these license changes are normally implemented with a major version, but we cannot assume that will always be the case. I will try to find an example.

[ljharb]

Perhaps we could encourage it by including a required "releaseVersion" in the event, that points to the relevant release event?