Add endpoints for add/replace/delete metadata

[kamorel]

Description

Adds new endpoints to add, replace, or delete metadata from an object. Each call will create a copy (and thus new version) of the object with the changes applied.

Types of changes

New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING doc
• I have checked that unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[jujaga]

A ton of missing semicolon and Do not access Object.prototype method 'hasOwnProperty' from target object warnings. For the latter, you can always just attempt to access the property directly, and then evaluate the truthiness of the value to see if it exists or not; don't need to invoke the hasOwnProperty method at all.

[TimCsaky]

looks good. Good that you did the controller and service as well for these!
i guess it would be better to add the tag related routes in another PR. And those controllers will work a bit differently.

not sure what we decided about the existing POST /object/:objId (to update an object) and whether you were able to modify metadata there as well. I think we discussed this: https://discord.com/channels/689896523848613952/689896524406194236/991494695609974855 probably could go in a separate PR. I think we should merge this soon.. unit tests could go in a separate PR.

[jujaga]

I think we may need to consider the deleteMetadata behavior some more. Current proposed implementation has it so that you must explicitly ask for each key to be deleted before it will be dropped. I see situations where it is possible the user would like to drop ALL metadata keys from an object but do not want to go back and explicitly figure out what was there. I think we should be able to support this use case - in which case, instead of returning a 422, its possible that by NOT specifying anything, we assume all metadata is to be dropped outside of our enforced values.

Let's chat a bit about some of the subtle edge cases offline but in general, it's looking pretty good otherwise. 👍