EDGAR healthcheck should validate GRE and Bridge

[mbfm]

EDGAR currently only pings the WireGuard IP-address. As such, it verifies that the VPN works, but cannot verify that the remaining openDuT-deployed configuration on the host works.
Instead, an IP-address should be assigned to a vETH interface, which's other end is hooked into br-opendut bridge. Then this IP-address should be pinged instead.

Tasks:

• [ ] Determine IP-address for each EDGAR in CARL. We may want to use IPv6 addresses and simply reserve a specific range, which we document.
• [ ] Send IP-address via PeerConfiguration to EDGAR.
• [ ] EDGAR creates vETH interfaces and hooks one end into br-opendut and assigns the IP-address to the other end.

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The following tasks have been completed as part of #329:

• [ ] ~~EDGAR is sent the IP-address of all other hosts that it should be able to reach in a new parameter, e.g. PingCheck(["123.456.789.012", "222.222.222.222"]).~~
• [ ] ~~EDGAR pings these IP-addresses instead.~~
• [ ] ~~See, if we can remove the list of addresses of other peers from the OldPeerConfiguration.~~