refactor(IDX): remove --container-cmd

[cgundy]

This changes the logic of the container-run.sh script back to what it was before by removing --container-cmd and detecting the container command based on environment. This removes some complexity but can be changed in the future if necessary.

[basvandijk]

Out of curiosity: do cases exists where users actually specify --container-cmd?

In other words: is there a reason we can't simply remove --container-cmd?

[cgundy]

Out of curiosity: do cases exists where users actually specify --container-cmd?

In other words: is there a reason we can't simply remove --container-cmd?

Yeah that's a fair point, since users can also just pass in arguments without specifying --container-cmd. My original intention was to align the inputs with build-image.sh which does accept --container-cmd (though it doesn't accept an additional argument). So I agree with you, it would make more sense to remove it completely. Let me take another look at this.