Support custom attributes and tags for crashes

[maxirosson]

We should be able to configure custom attributes and tags for crashes.

We could set a kind of builder to the exception handler, so tags and attributes can be defined by the SDK clients:

public interface CrashBuilder {
    fun buildTags(thread: Thread, throwable: Throwable): List<String>
    fun buildAttributes(thread: Thread, throwable: Throwable): Map<String, Any?>
}