ServerClusterInterface: decouple Ethernet Diagnostics Server

[andy31415]

Part of #36538

Modularize https://github.com/project-chip/connectedhomeip/blob/master/src/app/clusters/ethernet-network-diagnostics-server/ethernet-network-diagnostics-server.cpp

Since this already uses AAI exclusively, no special storage logic is needed (it does not depend on storage logic decoupling).

https://github.com/project-chip/connectedhomeip/tree/master/src/app/clusters/ota-provider can be used as an example of decoupling, generally we expect:

• a BUILD.gn file that defines stand-alone cluster definitions based on ServerClusterInterface
• a tests/ unit testing folder that exercises some of the cluster logic
• a CodegenIntegration.h/cpp that performs ember-specific integration (e.g. register/unregister and initializing IsLocalConfigDisabled to a proper value at boot time)

We generally need to update both AAI & command handling to be processed through the server cluster interface.

• Need to make sure this still works with ember dynamic clusters (see OTA provider example)
• Conversion of this cluster should help in determining flash/ram overhead of converting a cluster and determining any strategies to minimize this cost.