Add "callback" cluster click behaviour

[cwsiteplan]

It would be nice to have a click behaviour that performs the default zoom action but acts as a callback too. (so apps can perform certain side-effects when clusters are clicked.

[p-lr]

The name "Callback" doesn't convey that the default behavior is also triggered (even though the documentation is explicit). I would rather add a parameter to the existing Custom case, instead of introducing a new behavior:

internal data class Custom(withDefaultBehavior: Boolean = false, val onClick : (ClusterInfo) -> Unit) : ClusterClickBehavior

This would be an api change. However, cluster api is still experimental -- so this is acceptable. What do you think?

[cwsiteplan]

Yep, thought of that as well. Sounds good - will adapt my PR. 👍

[p-lr]

Thanks!