Add support for setting the storage size of the PV used by a workflow step

[flaviodsr]

Training a ML model usually requires copying remote data into the local storage (a persistent volume in kubernetes) where it will be used for training. The amount of storage required for storing this data varies, however FuseML does not provide a way to specify the size of that storage, instead, FuseML hardcodes that storage size (2 GiB, see: https://github.com/fuseml/fuseml-core/blob/main/pkg/core/tekton/constants.go#L8). Consequently, FuseML cannot be used for training models with more than 2 GiB of data.