DOC-4757 list async examples

[andy-stark-redis]

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DOC-4757

Couple of things to note:

• I've used exceptionally() in the rule_1.1 example to handle the exception that it demonstrates. Is this best approach? There seem to be a few ways to handle exceptions with CompletableFuture.
• I've hidden the del() commands at the start of some of the examples because they are hidden in the examples for the other clients/languages. However, would it be better to actually show the del() calls for Lettuce, given that the CompletableFuture instances are chained together? In some examples, the first line basically tells you the name of the previous example in the chain, so would readers assume that the new example starts with the same DB state that the previous one ended with?