Remove int cast that prevents setting redis database from env var

[jcerri]

Setting redis database from env var is impossible today due to int casting since the var has not been interpreted by symfony yet.

[greg0ire]

Please associate your email address with your Github account, or change the email in your commits to an address already associated with it.

[Majkl578]

My only concern is that what previously seemed valid: database: "default" would now throw an exception.

[aubryfr]

Indeed. Even though, as far as I understand, default would not be a valid value for a Redis database index.

What if we keep it as a scalar node and don't cast it to an integer? It seems like it would cover what Redis expects, not alter any meaningful value, and not break what the bundle currently accepts. But it needs to be tested.

[Majkl578]

It wouldn't be valid but the int cast would've hidden that problem by simply concerning it to zero.

[alcaeus]

Closing here for the reason stated in #156.