dandiset.yaml: add "standards" section?

I envision it to be primarily an auto-populated (e.g. using `dandi organize`) list of records with fields

- `name`: name of the standard (`nwb`, `bids`, `dandiset`, `dandi-layout` if we do not enforce, ...)
- `versions`: string or a list of strings - versions of the corresponding standard found in the dandiset (e.g., .nwb files could be a cocktail of NWB versions)
- `extensions`: a list of detected extensions to the standard (e.g., could be NWB extensions, nifti extensions, etc) probably again as a list of records with `version` field.
- `options`: this one is debatable one. I thought to (ab)use it to e.g. describe `dandi-layout` options (minimization of keys, or entire filename pattern, etc).

It might be that it would even relate to the "scope" aspect (#1) but likely it is too inherent within dandiset.yaml itself, and should eventually be described there.

Purpose: provide overview in the used standards. Could simplify search for datasets of particular qualities (bids, or the ones consistently layed out with `dandi organize`) .