ETag support

[dchanman]

We have a use case where we are considering ETags as a mechanism for supporting caching Redfish resources. At the moment, it doesn't seem like libredfish supports HTTP ETag.

We were just wondering if there would be interest in ETag support, and whether there were already some considerations or constraints that were considered for this feature.

[pboyd04]

Right now libredfish always goes and gets the latest copy of everything without caching. If you wanted to add a caching layer than etag would certainly be useful. I also haven't run in to any implementations that require If-Match headers so we haven't done that yet either, but it could be added.

[jautor]

We'd certainly welcome any additional functionality to the library!