Meta: `onyo_get` support for directories and templates

[aqw]

This is a tracking, meta issue to allow onyo get to select the type of data source to query (other than just assets).

The objective is to add support for directories and templates. This result would obviate the need for an onyo list (#53), onyo template (#552), and address #672.

• [ ] #676 (default to asset; the present behavior)
• [ ] #674
• [ ] #675

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Open Questions:

• what are the implications for onyo set and onyo unset
  • they both exclusively operate on assets (which is very, very sane)
  • but if one can query template keys, one naturally expects that one can set them...

[bpoldrack]

but if one can query template keys, one naturally expects that one can set them...

Seems valid to me. I think this would suggest to add a --type=template|asset to set, unset and potentially even new. I'd give that low priority ATM, though.

[nhjjr]

I'm in favor of this; I missed this recently when adding devices but wasn't sure what the templates were called. It's of course solved with ls .onyo/templates but that's only because I already know where the folder is located.

[aqw]

Yeah, tab completion is meant to alleviate this somewhat when creating assets with onyo new. But I agree that it's an incomplete solution.