Require NU5 checkpoints regardless of zebrad.toml settings

[teor2345]

Motivation

Mainnet nodes must check that their chain contains NU5 before:

• risking funds, including mining
• displaying transactions to users, including through lightwalletd

Ticket #5912 fixes this issue for the default config, so this is a low priority. It only affects configs generated before March 2022, or manually edited configs.

Specifications

A network upgrade is settled on a given network when there is a social consensus that it has activated with a given activation block hash. A full validator that potentially risks Mainnet funds or displays Mainnet transaction information to a user MUST do so only for a block chain that includes the activation block of the most recent settled network upgrade, with the corresponding activation block hash. Currently, there is social consensus that NU5 has activated on the Zcash Mainnet and Testnet with the activation block hashes given in § 3.12 ‘Mainnet and Testnet’ on p. 20.

https://zips.z.cash/protocol/protocol.pdf#blockchain

Complex Code or Requirements

We already have a mandatory checkpoint height, we just need to increase it.

We could also just ignore the checkpoint_sync setting, but that is more complicated, and it would make our CI images larger. (And maybe make the tests take longer.)

Testing

This has an existing CI test, we'll need to make the regenerate-stateful-disks job into a long test:

1. zebra/.github/workflows/continous-integration-docker.yml

   Line 353 in e78c5c5

   regenerate-stateful-disks:

   zebra/.github/workflows/deploy-gcp-tests.yml

   Lines 30 to 34 in e78c5c5

   	is_long_test:
   	required: false
   	type: boolean
   	default: false
   	description: 'Does this test need multiple run jobs? (Does it run longer than 6 hours?)'

2. And then run it manually using "run workflow" on the branch for this ticket: https://github.com/ZcashFoundation/zebra/actions/workflows/continous-integration-docker.yml

Related Work

Follow up to:

• On startup, check that the finalized state blocks match the checkpoint hashes #5912