RedfishPkg: Rename x-uefi-redfish to x-UEFI-redfish

Rename x-uefi-redfish to x-UEFI-redfish to match the format of
UEFI configuration namespace prefix.

RFC: https://edk2.groups.io/g/rfc/message/849



Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
Co-authored-by: Nickle Wang <nicklew@nvidia.com>
Cc: Abner Chang <abner.chang@amd.com>
Cc: Igor Kulchytskyy <igork@ami.com>
Cc: Nick Ramirez <nramirez@nvidia.com>
Reviewed-by: Abner Chang <abner.chang@amd.com>