node-proxy: split redfishdell class

node-proxy: split redfishdell class

This refactors split the redfishdell class in order
to collect power and thermal details from the redfish API.

'power' and 'thermal' details are very different in many points:

- not available at the same endpoint,
- data structure is different.

For these two reasons, let's split that class.

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>
(cherry picked from commit db0172186a753d57c357a5396378d1158e3167e3)