Fix metric setting of nmconnection for rhel

[xiachen-rh]

Most RHEL systems use network manager to bring up manage network connections.
Network Manager uses route-metric for the default route and route/plen[,gateway,metric] for the additional static routes, please see
https://networkmanager.dev/docs/api/latest/nm-settings-nmcli.html
https://networkmanager.dev/docs/api/latest/nm-settings-keyfile.html

This changes ensures that cloud-init generates nmconnection files with route metric settings that are compatible with RHEL and network manager.

Fixes: GH-5877

Test steps

For the config data

#cloud-config

network:
  version: 1
  config:
    - type: physical
      name: enp1s0
      subnets:
      - type: static
        address: 10.0.2.2/24
        gateway: 10.0.2.1
        routes:
          - destination: 0.0.0.0/0
            gateway: 10.0.2.1
            metric: 99
          - destination: 192.168.122.1/24
            gateway: 10.0.2.1
            metric: 98

After this changes the nmconnetion file looks as below

# cat /etc/NetworkManager/system-connections/cloud-init-enp1s0.nmconnection
# Generated by cloud-init. Changes will be lost.

[connection]
id=cloud-init enp1s0
uuid=a41601f3-3acc-5f60-ac5f-9d9011ab7c25
autoconnect-priority=120
type=ethernet
interface-name=enp1s0

[user]
org.freedesktop.NetworkManager.origin=cloud-init

[ethernet]

[ipv4]
method=manual
may-fail=false
address1=10.0.2.2/24
gateway=10.0.2.1
route-metric=99
route1=0.0.0.0/0,10.0.2.1
route2=192.168.122.1/24,10.0.2.1,98

and the routes are configured with metric

$ ip r show
default via 10.0.2.1 dev enp1s0 proto static metric 99 
10.0.2.0/24 dev enp1s0 proto kernel scope link src 10.0.2.2 metric 99 
192.168.122.0/24 via 10.0.2.1 dev enp1s0 proto static metric 98 

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[xiachen-rh]

Hi @ani-sinha, could you please help to take a review?

[ani-sinha]

If the metric value were added here, it would have been the same effect since it also specifies default route. I think we should do it this way instead of adding route-metric . In other words, there is no need to check for default route and add route-metric. All matric values can be added as a comma separated value.

[ani-sinha]

Not sure if we really want to add route-metric separately.