Introduce ErrNotSupported sentinel error for unimplemented vendor BMC methods

[coderabbitai]

Summary

Controllers such as internal/controller/bmcversion_controller.go and internal/controller/biosversion_controller.go call vendor-specific BMC client methods (e.g. CheckBMCPendingComponentUpgrade) and currently treat all errors identically — including the base RedfishBaseBMC fallback that returns a "not supported by this manufacturer" error. This means transient Redfish/FirmwareInventory failures are silently swallowed and the upgrade proceeds, which is the same behavior as a legitimate "not supported" response.

Motivation

Introducing a dedicated ErrNotSupported sentinel error would allow controllers to:

• Ignore the "not supported by vendor" case (current behavior, intentional)
• Requeue on transient or real check failures instead of blindly proceeding with the upgrade

This improves safety: a temporary FirmwareInventory unavailability would no longer silently bypass the pending-upgrade guard.

Scope

• Define an ErrNotSupported sentinel (e.g. in bmc/bmc.go or a shared errors file)
• Update RedfishBaseBMC.CheckBMCPendingComponentUpgrade (and similar fallback methods) in bmc/redfish.go to wrap/return ErrNotSupported
• Update affected controllers (bmcversion_controller.go, biosversion_controller.go, and any future controllers) to use errors.Is(err, bmc.ErrNotSupported) to distinguish the two cases
• Consider applying the same pattern to other vendor-specific BMC interface methods that currently have a "not supported" fallback

References

• PR Implement vendor-specific BMC/BIOS upgrade checks with firmware inventory function #733 (where this was first discussed): Implement vendor-specific BMC/BIOS upgrade checks with firmware inventory function #733
• Specific comment: Implement vendor-specific BMC/BIOS upgrade checks with firmware inventory function #733 (comment)

/cc @davidgrun