fix(wg create): break endless loop when file exists

[abitrolly]

Fixes #4665

Change Summary

What and Why:

This fixes endless loop in when supplied wg create filename already exists. The problem was caused by argOrPrompt helper, which always returns the command line argument if it is set, so the prompt never appears in this case.

How:

Added flag.GetArg(ctx, idx) helper to clean up the logic. Then reworked the loop so that it first checks for all favorable conditions, and then runs prompt without the helper that attempts to do too much.

Now if there is a problem with config file supplied as cmdline argument, flyctl enters the interactive prompt to allow to fix the mistake.

Related to:

#4665

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Documentation

• Fresh Produce
• In superfly/docs, or asked for help from docs team
• n/a