Add ThermalMetrics schema

Based on DSP8010_2022.2 and adds the ThermalMetrics schema.
ThermalMetrics is child of the ThermalSubsystem schema. It is part of
the new Power/Thermal Schemas.
ThermalMetrics contains temperature readings and the corresponding
link to that sensor in the sensor collection.
Temperatures such as Ambient, Exhaust, Intake, and Internal can be
found in the schema.

Tested: built bmcweb successfully and validator passes.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I16ad2f922acc963a0434f3d9ab5583d2242b0013