Allow setting of contentTemplate in configObj

[gustavlrsn]

It would be neat if I were able to use different templates for different alerts, by setting the contentTemplate in the configObj, like this:

Alert.success('Alert message', {
    contentTemplate: AnotherTemplate,
});

[samjhill]

+1, I would love this

[gustavlrsn]

@samjhill what I did instead was pass along a variable in customFields that the template itself then uses to render different variants