Add "locktime" and "ownername" to cs3 lock api

[kobergj]

The lock object should be enhanced with two new optional values:

• "ownername": The name of the lock owner. This is an enhancement so clients do not have to query for the owner name.
• "locktime": The time the lock was created. Additionally to "expiry" this gives more information to the clients.

See discussion in poc PR: cs3org/reva#4133

See lock object on current main: https://github.com/cs3org/cs3apis/blob/main/cs3/storage/provider/v1beta1/resources.proto#L159-L180

[labkode]

@glpatcern

[glpatcern]

From the discussion in the referenced PR, I understand that:

• For the ownername, it really seems an optimization due to lack of caching of the web layer. As such, an opaque extra value for now makes sense, whereas promoting this to a field seems sub-optimal. At least, it introduces room for contradictions if ownername does not correspond to the username of user, and that alone IMHO is a reason not to add this value.
• For the locktime, I don't have a very strong opinion. @tbsbdr mentioned that exposing the expirationtime is totally fine for web. @butonic do we really have an added value in specifying both values?