Improve CLI help handling for run command

[bm371613]

Updated the run command so that --help is passed to the subcommand if there is one.

Rationale

Many times I tried to run a subcommand, like

dotenv run some_command --help

and saw a help message from dotenv, and not the command.

I think it's common to

1. run an incorrect command
2. use a shortcut (like arrow up) to view the previous command
3. add --help to the previous command to learn about correct usage
4. use a shortcut (like arrow up) to view the previous command
5. fix the command

If dotenv takes over --help meant for subcommands, this workflow has to be changed by removing dotenv -f .some.env.

My change attempts to alleviate it.