Implement Custom Atmos Shell Prompts inside Geodesic

[coderabbitai[bot]]

As discussed in PR #827, we need to solve for custom Atmos shell prompts inside Geodesic.

https://github.com/cloudposse/atmos/blob/73c8c4959c65db66b7893ff3e23abad283a03ad1/internal/exec/shell_utils.go#L265-L270

[osterman]

@Nuru what if we added support for custom args to the shell, to make it more configurable:

In atmos.yml we already support a configuration section for the prompt.

components:
  terraform:
    shell:
      prompt: ...
      args: "-l"