Enabled plugins to detect devbox entrypoint and alter their behavior

[kadaan]

Summary

Extract getSubcommand from telemetry and use it to set the new DEVBOX_ENTRYPOINT environment variable in midcobra. Use the new env var in venvShellHook.sh to stop printing the banner when running via devbox run ...

Fixes: #1823

How was it tested?

Manually run a devbox with python package via both devbox shell and devbox run. When devbox shell is used, the banner is printed. When devbox run is used, the banner is not printed.

[kadaan]

Another example of a command that should not print the python banner:

❯ devbox services ls
You can activate the virtual environment by running 'source $VENV_DIR/bin/activate'
No services currently running. Run `devbox services up` to start them:

[kadaan]

@Lagoja @gcurtis @mikeland73 Can you offer some feedback on this? I'm game to change this if this is not how you want to approach it, but the banner messages are increasingly annoying.

[kadaan]

@Lagoja Any feedback?