[MCHANGES-412] Allow an action to carry an optional scope

**[Gary D. Gregory](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=garydgregory)** opened **[MCHANGES-412](https://issues.apache.org/jira/browse/MCHANGES-412?redirect=false)** and commented

In changes.xml, I would like an **action** to carry an optional {**}scope{**}.

This would help users understand what changes affect which part of their projects.

For example:

Fix some bug\
Bump dependency foo from 1 to 2\
Bump commons-parent foo from 1 to 2\
Documented this and that\

The use of the scope documents where the change applies, usually runtime, test, or build, but it could be string maybe.

This somewhat parallels the concept of a scope in a dependency so the value set could be the same as allowed for a dependency scope but that might be too restrictive.

Thoughts?

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No further details from [MCHANGES-412](https://issues.apache.org/jira/browse/MCHANGES-412?redirect=false)

Comienza con los ejemplos de action de changes.xml y sigue cómo se representan y consumen los atributos de action en el plugin. Define el comportamiento de scope cuando es opcional y sus valores aceptados; después, verifica que las acciones con scope sean aceptadas y que su scope sea visible para los usuarios sin romper las acciones que lo omiten.

Escrito por el modelo de indexación a partir del texto del issue.