Add a fallback to use sh instead of hardcoded bash

[shivam-clary]

In a lot of docker images like alpine based images, they only contain sh. They don't contain bash by default making it impossible to run any command using the execd. Here we can see the bash command is hardcoded. Can we instead have a way to either set a configuration from the client library or just a generic fallback to sh if it is not available?

OpenSandbox/components/execd/pkg/runtime/command.go

Line 96 in cbd22e6

cmd := exec.CommandContext(ctx, "bash", "-c", request.Code)