Add network upgrade config

[aaronbuchwald]

This PR replaces the constants/per-networkID getter functions for network upgrade timestamps with a network upgrade schedule struct and a single function to retrieve the corresponding upgrade schedule.

• Update Coreth dependency
• Support configuring upgrade schedule via CLI flags

[aaronbuchwald]

This is failing due to https://github.com/ava-labs/coreth/pull/613/files#r1694251921

[aaronbuchwald]

I think that 1) passing the full upgrade struct around as needed instead of individual upgrade times including adding it to *snow.Context for each VM and 2) updating coreth to align the default local network fork activation times with AvalancheGo should be follow up PRs.

[ceyonur]

how do we pass this new config to VMs? For instance Subnet-EVM also has a overridable config that depends on avago's values for networks. I'm not sure if this is strictly required to be correctly supported since this is only for custom networks (I assume for testing).

[ceyonur]

I think we can even disable this option if we're running any subnet.

[StephenButtolph]

This will be added to the snow.Context in a followup.