Add `cache` configuration key documentation

[boesing]

Feature Request

Q	A
Documentation	yes

Summary

There is a cache config key which can be used for some kind of "default" cache adapter for a project.

laminas-cache/src/Service/StorageCacheFactory.php

Line 19 in fcc91ac

$cacheConfig = $config['cache'] ?? [];

Not yet a clue where this is used for, might be an MVC specific thing 🤷🏼‍♂️

[froschdesign]

@boesing
I find it difficult to explain to the user that they can use caches and also cache. Because already the first one leads to the desired result and also only works with a single cache. So the question is: Is this factory really needed?

[boesing]

So the question is: Is this factory really needed?

@froschdesign I am not sure, could be dropped in v4 and we can see how this adds up.
I'd also recommend to use some kind of StorageInterface::class => 'entry-in-caches-array', aliases entry instead if someone needs a default cache adapter as that would avoid having a redundant cache configuration laying around somewhere.

[froschdesign]

Any simplification or removal of confusion is welcome and absolutely necessary. I also think that the improvements implemented here must then be transferred to other components.