luci-proto-yggdrasil: add `yggdrasil-jumper` support

[one-d-wide]

Description:

Yggdrasil Jumper is independent project that aims to transparently reduce latency of a connection over Yggdrasil network, utilizing NAT traversal to bypass intermediary nodes. It periodically probes for active sessions and automatically establishes direct peerings over internet with remote nodes running Yggdrasil Jumper without requiring firewall or port configuration.

Changes:

• Add Jumper tab to yggdrasil interface configuration.
• Add rpcd calls to check if jumper is installed and verify user provided configuration.