Support ability to disconnect from backend manually

Following up on the conversation on #131, I’m using keyv from a one-off script and the Node.js process hangs because there’s an open socket.

I’m having to (partly) work around this by doing the following:

    const redis = (this.keyv.opts.store as KeyvRedis).redis;
    redis?.disconnect();

… which isn’t ideal because my code is now Redis-aware and would still break when we support additional backends.

@jaredwray mentioned there’s some interest in implementing Keyv.disconnect(), which would cause the underlying backend to disconnect from the server. That would solve this problem.

[jaredwray]

@gnarea - This is currently being tracked in a pull request by @alphmth here: https://github.com/jaredwray/keyv/pull/307

[gnarea]

This is fantastic! Thank you so much!