Make fragment size of preset configurable through GUI

[kinvaris]

Currently we have to create a preset through the CLi if we want another fragment size.
In the GeoScale perspective, it would be interesting to make the fragment size of the preset configurable during creation/update.

[domsj]

FYI: updating the fragment size of an existing preset is currently not supported by alba.
If you need that (and maybe allow updating compression/encryption/name and others(?) too while at it): please file a ticket for alba too.

[domsj]

This is important for global backends: you definitely want a bigger fragment size there.

[openvstorage-ci]

This issue was moved to openvstorage/framework-alba-plugin#204