Add Kotlin to examples

[QuintinWillison]

In the same way that we have Swift illustrated in addition to Objective-C for ably-cocoa examples, we should have Kotlin illustrated in addition to Java for ably-java examples.

We've already seen one customer support issue (internal link: 105418) where the fact that Kotlin doesn't have/need a new keyword caused confusion in that the nested class Channels in AblyRealtime could 'accidentally' be instantiated via constructor rather than accessed via field - i.e. the difference between myAblyRealtimeInstance.Channels() (constructor) and myAblyRealtimeInstance.channels (field).

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