feat: Migrate networks to yml file (1 of 2)

[activescott]

Submission for milestone B of bounty BA0902402 to move networks to yaml.

The networks-default.yml file is in rocket-pool/smartnode-install#122

fixes #438

@jshufro Can you please review and make sure this is on the right track. I think this is complete. The things that are on my mind though:

• Not super clear what would be an effective set of tests as much of that data is used in operations that I'm not sure how to easily/quickly exercise. If you want to suggest some test cases I'm happy to run them. I was able to use rocketpool service config and restart my holesky node and it seems fine.
• Am I missing some other places where network info is needed?

[activescott]

@jshufro Added substruct. I also noticed I forgot to add support for extra-networks.yml and did that and tested it. Please let me know what else needs done here to get this one merged.

[activescott]

Hey @jshufro. You mentioned holding off on this. Should I pick up those changes from comments and see this through or is the consensus that we should no longer do this?

[jshufro]

I think the best thing would be to rebase onto the v2 branch. A lot of the work unfortunately won't apply, but the good and bad news is that this was already incomplete- https://github.com/rocket-pool/smartnode/pull/459#pullrequestreview-1935169929 I do think for this to be meaningful we need to be able to add networks simply by adding yaml