allow importing labels from a given file in mod-script-pipe

### Your idea

When you need to import an audio file using mod-script-pipe **non-interactively**, you can use the command [Import2](https://manual.audacityteam.org/man/scripting_reference.html#:~:text=just%20one%20command.-,Import2,-%3A).

Unfortunately I failed to find an equivalent for importing **labels**. There's only [ImportLabels](https://manual.audacityteam.org/man/scripting_reference.html#:~:text=your%20existing%20project.-,ImportLabels,-%3A)
which opens a file selection dialog.

Is there a way to import a label track skipping an interactive dialog?

### Problem to be solved

Allow to import label files non-interactively.

### Prior art

_No response_

### Additional context

_No response_

Start with the mod-script-pipe entry point and compare the non-interactive Import2 command with ImportLabels in the scripting reference. Trace how ImportLabels currently opens its file selection dialog and determine the command shape needed to accept a label file directly. Done means label files can be imported non-interactively through mod-script-pipe while the existing interactive behavior remains usable.

Written by the indexing model from the issue text.