Add contentId to asset metadata

[yarikoptic]

I think it should complement contentType which I proposed to introduce in

• Introduce ContentType as Blob vs Zarr and rename blobDateModified to contentDateModified #220

Note that we might need to decide to either make it prefixed, such as blob:{blob_id}, dandizarr:{zarr_id} or just those ids.
This was inspired by the need to use such, ideally avoiding choosing and parsing contentURL for

• External services for "Open with" for zarrs to browse them: add quiltdata dandi-archive#2655

[satra]

the user/script should figure this out without coding more semantics into names. the information passed to "open with" with already has semantics, params could be added as we have discussed and implemented with @magland in the past. let's perhaps focus on ensuring contentType is properly populated instead of introducing rigid semantics in some other place.

[yarikoptic]

what do you mean by "semantics" here since from your response I thought you are against introducing contentType in the

• Introduce ContentType as Blob vs Zarr and rename blobDateModified to contentDateModified #220

Hence I feel that we are ATM unnecessarily "hiding away" one of the core semantical differences of blobs-vs-zarrs, and indeed trying to avoid to expose their unique identifiers we have within the archive (exposed only within contentURL).