L2 subnet topology + netcfg CLI

[GandalfTea]

Summary

This PR adds support for a low-level L2 network creation between peer nodes that avoids the broadcast storms from #69

Changes

• API Node builds a low-level L2 network topology plan during prepare_topology call from the solver-level generated topology. It then transmits this plan as JSON routes to workers.

• Shard Nodes receives the JSON plan and invokes the new dnet-netcfg tool (bridges, /31 addressing, routes, MTU rate, etc.)

• netcfg: new macOS CLI that:

  • intakes plan from shard node in JSON form and applies it, validates it and optionally creates a new network service to persist interfaces across reboots.
  • handles virtual bridge creation/destruction, member iface attachment/detachment, changes MTU rate, updates routing table.
  • tests connections with pings, routes and iperf3 speeds.

• netcfg requires sudo for some commands. It fails with permission errors on which the API Node prompts the user for the password of that specific peer. Once a password is given once netcfg registers itself with NOPASSWD via visudo in sudoers. It also moves itself in /opt/homebrew/bin because of the safe path requirement of visudo and modifies it's permissions.

• unit test netcfg tool

Type of Change

Mark the relevant option with an 'x'

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• CI/CD improvement

Testing

Describe the tests you ran and/or how to test these changes

• Tests pass locally
• Added new tests for the changes
• Existing tests updated

Checklist

• My code follows the project's code style
• I have made corresponding changes to the documentation

Closes #

#69