Provide tab-completion for `leeway run`

[mads-hartmann]

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Is your feature request related to a problem? Please describe

Currently tab-completion for Leeway doesn't work for "scripts", so leeway run <tab> will just give you normal shell tab-completion.

Describe the behaviour you'd like

leeway run <tab> should suggest all scripts in any leeway component in the workspace.

Describe alternatives you've considered

I haven't considered any alternatives.

Additional context

Nope