Allow optional `profile` to be specified in `CREATE_DISK` offer operation.

This will allow the framework to "import" pre-existing volumes reported by the corresponding CSI plugin.

For instance, the LVM CSI plugin might detect some pre-existing volumes that Dan has created out of band. Currently, those volumes will be represented as RAW "disk" resource with a volume ID, but no volume profile by the SLRP. When a framework tries to use the RAW volume as either MOUNT or BLOCK volume, it'll issue a CREATE_DISK operation. The corresponding SLRP will handles the operation, and validate against a default profile for MOUNT volumes. However, this prevents the volume to have a different profile that the framework might want.

Ideally, we should allow the framework to optionally specify a profile that it wants the volume to have during CREATE_DISK because it might have some expectations on the volume. The SLRP will validate with the corresponding CSI plugin using the ValidateVolumeCapabilities RPC call to see if the profile is applicable to the volume.