net: add route-metric support in NetworkManager renderer

[Harshadev-24]

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Proposed Commit Message

fix(net): add route-metric support in NetworkManager renderer

This implements the `route-metric` configuration for the NetworkManager 
renderer when a `metric` value is provided in the subnet data. Prior to 
this, the renderer was silently ignoring the route metrics provided 
by the cloud data sources.

Fixes GH-6854

[challvy]

this PR is releated to this issue #6854

[challvy]

Hi @holmanb , @blackboxsw — would either of you have a moment to review this PR? Thanks in advance!

[holmanb]

Please address the failing tests.

[Harshadev-24]

@holmanb Just a heads up, the check_format CI is currently failing on tests/unittests/config/test_cc_phone_home.py (Line 57) due to an E501 line length error. Since this is outside the scope of my changes in the NetworkManager renderer, I believe this is an upstream issue on main. My formatter fixes for test_network_manager.py are pushed and ready. Let me know if you need anything else from me!

[holmanb]

@holmanb Just a heads up, the check_format CI is currently failing on tests/unittests/config/test_cc_phone_home.py (Line 57) due to an E501 line length error. Since this is outside the scope of my changes in the NetworkManager renderer, I believe this is an upstream issue on main. My formatter fixes for test_network_manager.py are pushed and ready. Let me know if you need anything else from me!

Please rebase or merge on main. I believe that this was already fixed.

[holmanb]

Looks good, thanks for the proposal!