Provide Overview data for visualization in the Dashboard

[Lachstec]

We need to provide metrics of the siblings in order to visualize them in the Dashboard. Metrics can be acquired via gNMI, so we just need to know what data would be nice to have.

@RedEagle-dh can you reply with a selection of data that would be nice for you? We can then build a gNMI Query to retrieve it and make it available for you via a Queue or something along the lines.

[Lachstec]

Ideas from us:

• /system/state => Uptime, Software Version, Hostname
• /interfaces => List of Interfaces with packet counters, current state, MAC-address, etc.
• OSPF Information (unknown path)
• Static Routes

[RedEagle-dh]

For the topology the following data is important:

• nodes & links
• general node data (e.g. ipv4, ipv6, mac, ...)
• general link data (e.g. connected nodes, connected endpoint (e,g, eth1))
• current traffic over a node & link
• current node status
• for the future maybe realnet-data of the node (e.g. temperature)

Don't know if everything is possible but thats all I'd need for now. Maybe you can reply what would be possible from the selection above :)

[Lachstec]

The first three things are definitely possible, but i am unsure about the latter three. Maybe they are tricky / not possible to provide, but i will let you know if i find anything out.

[S-Schickentanz]

Added branch node-overview to work on providing overview data.
For now, it is implemented as an app that runs on the siblings and provides data depending on the overviewPaths provided in the digsinet.yml