Bring gateway config files closer to normal locations

[FFHener]

This was decided on our community day February 2024.

We have a way of describing management, uplink and mesh Interfaces for locations and should consider using the same format for the gateways. This will require changing some templates as well as having a look if we could combine templates that are present for corerouter and gateway role into one common template. This could reduce code duplication.

Edit templates:

• bird.conf.j2
• config/firewall.j2
• config/dhcp.j2
• config/olsrd.j2
• config/network.j2 -> wip
• conntrackd/conntrackd.conf.j2
  ...

Check if output is still the same for corerouters and gateways:

• bird.conf.j2
• config/firewall.j2
• config/dhcp.j2
• config/olsrd.j2
• config/network.j2
• conntrackd/conntrackd.conf.j2

Locations:

• ak36
• l105
• ohlauer
• saarbruecker
• strom