Mandatory ext-memcached

[Huluti]

Hello,

Thanks for your work!
Just having a small issue on my side since several versions.
I can't upgrade the package since one of your dep require a php extension:

    - Root composer.json requires utopia-php/domains ^1.0 -> satisfiable by utopia-php/domains[1.0.0].
    - utopia-php/cache 1.0.0 requires ext-memcached * -> it is missing from your system. Install or enable PHP's memcached extension.

I think ext-memcached should be optional no? Not all servers have this extension installed.