Add option for size of the preflight PVC

[nikdoof]

I'm currently migrating some manual iSCSI PVs to Democratic-CSI managed iSCSI PVs, one of the problems I've hit is that 1Mi is too small for xfs filesystems to format correctly with the block size setup I have.

Building a custom version of pvmigrate with the PVC size bumped to 100Mi worked. It would be nice if we had a argument to pass in the preflight PVC size to avoid this issue.

[laverya]

Another alternative here is to run with --skip-preflight-validation - that'll skip the preflights entirely.

I agree with the desirability of the option to run with a different size, though.

[ledroide]

I am experiencing the same issue with a netapp-trident backend.

volume pvc-d471b3e6-96ff-4455-ba6e-91b8fca79a13 on storage pool n11_aggrNLSAS_01 from backend ontap-nas: unsupported capacity range; requested volume size (1048576 bytes) is too small; the minimum volume size is 20971520 bytes]; [Failed to create volume pvc-d471b3e6-96ff-4455-ba6e-91b8fca79a13 on storage pool n10_aggrSSD_01 from backend ontap-nas: unsupported capacity range; requested volume size (1048576 bytes) is too small; the minimum volume size is 20971520 bytes]; [Failed to create volume pvc-d471b3e6-96ff-4455-ba6e-91b8fca79a13 on storage pool n09_aggrSSD_01 from backend ontap-nas: unsupported capacity range; requested volume size (1048576 bytes) is too small; the minimum volume size is 20971520 bytes]; [Failed to create volume pvc-d471b3e6-96ff-4455-ba6e-91b8fca79a13 on storage pool n12_aggrNLSAS_01 from backend ontap-nas: unsupported capacity range; requested volume size (1048576 bytes) is too small; the minimum volume size is 20971520 bytes]