[Design] Use @Redfish.Settings to support pending settings in Computer System

[nicklela]

We can use @Redfish.Settings to support pending settings in Computer System if there is no ETag support. Some vendor BMC already support @Redfish.Settings in Computer System schema.

[nicklela]

Reason why BMC team does not like this idea:

• Allowed method for /redfish/v1/Systems/system is GET and PATCH. User can still make patch to computer system resource
• User is not familiar with using @Redfish.Settings for /redfish/v1/Systems/system. User may feel confused.

New design:

• BIOS manages the “Boot” attributes at /redfish/v1/Systems/system/
• BIOS track the change to “BootOrder” UEFI variable and decide synchronization direction:
  • Push boot order to BMC when BootOrder is updated in setup menu or OS
    • Overwrite boot order change from BMC because the boot order on BMC is not accurate anymore
  • Consume boot order from BMC when BootOrder is updated by user