Add `reason` to `@Characterization`

[ayeseeem]

Would allow us to add an informational string to the annotation.
This could be available for later processing, so might be different from - or instead of - expressing it in the test name.

For example:

@Characterization("DB returns null not empty")
public void testItemNotFound() {
    // ...
}

[ayeseeem]

There is now a value attribute, which does not have to be explicitly specified, so you can write

@Characterization("Some reason")

You don't have to write

@Characterization(value = "Some reason")

However, you (still) cannot use reason in place of value.

Note that Spring has an annotation
@AliasFor
that looks interesting.
Don't want to need to use Spring, but would be interesting to see how they do it.

[ayeseeem]

Closed when value attribute was added, but re-open because being able to specify reason still might be nicer.