[enhancement]: Reopen PR #6097 to add keep_configuration as a netplan option

[uhryniuk]

Enhancement

The PR #6097 was originally opened by @a-dubs which included changes to help enable IPv6 on Oracle cloud instances. The PR was closed due to "this change is no longer necessary (for the time being) due to similar functionality existing in initramfs-tools on noble+ (ubuntu 24.04 and forward)." as mentioned by @a-dubs

However, with dracut being considered to replace initramfs, it appears will need these changes implemented to aid that transition for Oracle Cloud.

[TheRealFalcon]

I opened #6307 and we can continue the work there.

[a-dubs]

@TheRealFalcon I'm happy to own these changes and finish them out. Especially considering any changes needed to close out the PR will be minimal. I can just reopen the original PR? Or should I open a new one

[TheRealFalcon]

@a-dubs , thanks! I opened #6307 as I figured it'd be easier for us to make any additional changes separately, but if you really want to, feel free to re-open yours.

[a-dubs]

@TheRealFalcon I'll re-open my original one. Since i think it shows some important decisions that were made along the way that lead us to that final implementation - i think this is helpful given how confusing that work was the first time around anyway.