Add uption to create (POST) metadata in update_metadata function in the resource class

This MR fixes the update_metadata function in the fact that there is no way to create metadata for existing file objects in Coscine that do not have metadata assigned yet (e.g. in RDS-S3 resources). The function doc string did state it handles this, but this was not the case.

Furthermore, I have also included an option to overwrite files or not in the upload function (may have been smart to do this in another MR... I could revert and split things, let me know).

@romin.benfer this actually contains all the things from !18 (merged), so I guess if you agree with everything in these two MR you could just merge this one.

Per our discussion in the other MR, I double-checked and resource.file('filename').post_metadata() doesn't work I noticed the docstring in the update_metadata function also states that it will use the post_metadata() function if the metadata needs to be created, but this was not the case.

Hey @romin.benfer any thoughts here and on !18 (merged)?

@nikkiaparks I'm eager to test this but the testing pipeline is currently not functional as some runners on the testing instance are offline. I'm currently asking around as to why that is the case.

Thanks for the update!

@romin.benfer We still need to solve this problem. I tried using the `resource.file('filename').assign_metadata(metadata_graph), but I don't quite understand that function..

IIRC it assigns the metadata locally without updating it remotely (it does not send the changes to Coscine).

Resolved with 382df894

closed