Fix Redis container to accept input command

[ziggornif]

Hi,

Here's a small fix to resolve the Redis container startup issue with custom commands (#1150).

I noticed a similar issue with the redis-stack image that also overrides this.createOpts.Env.
Would you prefer I include this fix in the same PR, or should I create a separate issue to track it first?

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[cristianrgreco]

Hi @ziggornif, yes please include the redis-stack command change in this PR

[ziggornif]

Hi @cristianrgreco, I just made the modification for redis-stack as well. The REDIS_ARGS variable now contains the merge of the user's values with the default values.

I kept the current solution of creating the variable via this.withEnvironment which I recreate with the merge of both values.
We could have also edited the existing variable in this.createOpts.Env. If the current solution works for you, I'll leave it as is.