Versioning field in the context part is confusing, maybe rename to specversion

[m-linner-ericsson]

The version field https://github.com/cdevents/spec/blob/main/spec.md#version specifies that it defines the version of the specification. Also the https://github.com/cdevents/spec/blob/main/spec.md#type-context specifies that is should contain the version of the event. When looking at a event this is super confusing.

Proposal is to rename the version filed to something more descriptive that describes that it specifies the specification version. Maybe rename it to spec_version.