Do update dandisets' "modified" timestamp whenever assets metadata "gets fixed"

[yarikoptic]

A number of dandisets got their assets metadata updated but dandiset time stamp was not modified.

I believe due to

• Derive asset access field from asset blob #2010
  fix we got now changes like this in metadata records

    | --- old-metadata
    | +++ new-metadata
    | @@ -5,7 +5,7 @@
    |    '@context': https://raw.githubusercontent.com/dandi/schema/master/releases/0.6.6/context.json
    |    access:
    |    - schemaKey: AccessRequirements
    | -    status: dandi:OpenAccess
    | +    status: dandi:EmbargoedAccess
    |    approach:
    |    - name: electrophysiological approach
    |      schemaKey: ApproachType

Some might argue that metadata "fixes" should not result in dandiset "modified" time but in the current model IMHO they should. Without that API would not provide reliable means for efficient monitoring/mirroring of the archive (as we e.g. need for backups2datalad) since it would be impossible to rely on "modified" timestamp as indicator of having or not changes in the dandiset. Could

• functionality introduced for Derive asset access field from asset blob #2010 be adjusted so to trigger corresponding dandiset(s) modified time stamp be adjusted
• do adjust "modified" for modified in that fix dandisets
  ?

[yarikoptic]

Similarly now happened due to a fix for .json files not having correct encodingtype.

IMHO there should be a generic interface which would ensure that mtime is adjusted if there are such mutations.