Integrate BMC support and Redfish APIs into SONiC (#605)

Additional BMC-related PRs:
sonic-net/sonic-utilities#4104
sonic-net/sonic-buildimage#24345

Description
This PR introduces a new BMC base implementation in the SONiC platform common layer
to provide a generic interface for BMC management using Redfish APIs.
It adds a reusable Redfish client and integrates BMC handling into the chassis base class.

Motivation and Context
There was no unified way for SONiC platforms to interact with BMCs.
This change introduces a common Redfish-based BMC interface, enabling:

Consistent and reusable BMC operations across platforms.
Simplified platform-specific extensions by inheriting from BmcBase.
Integration with higher-level SONiC features (e.g., show platform bmc CLI, techsupport BMC dump collection).

How Has This Been Tested?
Verified instantiation of the BmcBase object through the chassis platform API.
Confirmed successful Redfish communication with the BMC using the new RedfishClient.
show platform firmware status
show platform bmc summary
show platform bmc eeprom
show techsupport
config platform firmware install chassis component BMC fw -PATH-

Author: benle7

sonic_platform_base/__init__.py

@@ -10,3 +10,4 @@
 from . import thermal_base
 from . import sensor_base
 from . import watchdog_base
+from . import bmc_base