storage: allow sending metadata with CreateDir and Upload requests

[butonic]

We should allow sending MD Metadata with

• FS.CreateDir and
• FS.Upload to send along the original ctime and mtime as well as extended attributes.

Furthermore, we need to be able to manipulate metadata, in order to

• implement touch()
• set extended attributes

[moscicki]

@butonic: correct. we are cleaning all these things up properly on the review branch.

[labkode]

@butonic the opaque field helps in this case, for example here:
https://github.com/cernbox/cs3apis/blob/review/cs3/storageprovider/v0alpha/storageprovider.proto#L157

If we know that there will be logic used by many implementations then those use-cases can be promoted to non-opaque fields.

[moscicki]

We should add attributes to ExtraMetadata wherever it makes sense and does not depend on particular storage backend:

https://github.com/cernbox/cs3apis/blob/review/cs3/storageprovider/v0alpha/resources.proto#L138

I would avoid creating too many hidden stuff in Opaque because it will be breaking the "standard".

[labkode]

We should add attributes to ExtraMetadata wherever it makes sense and does not depend on particular storage backend:

https://github.com/cernbox/cs3apis/blob/review/cs3/storageprovider/v0alpha/resources.proto#L138

I would avoid creating too many hidden stuff in Opaque because it will be breaking the "standard".

If many storage back ends support it