Allow to create separate upgrade schedules for different chain ids

[jancionear]

A ProtocolUpgradeVotingSchedule defines when neard starts voting for new protocol versions. The voting date is set globally, no matter whether it's mainnet, testnet or something else. Because of that we have to make release-specific commits for every testnet and mainnet release. First we have a commit that sets the voting date for testnet, then a commit which removes the testnet voting date and sets the mainnet voting date.

I think it'd be nicer if we could have separate upgrade schedules for each chain id - we could say that testnet should vote at this time and mainnet should vote at this one.

Advantages:

• Less chaotic code which removes and sets voting dates on the release branchs
• Harder to make a mistake and e.g set a testnet voting date in a mainnet release
• Ability to run protocol upgrade tests on the exact version of neard that is published in the release. Currently integration tests fail when the protocol version is set, AFAIK we also have to change something about it for mocknet tests. With per-chain protocol upgrades this wouldn't be a problem - there would be no voting date set for localnet and mocknet chains.
• Ability to release the same release to both testnet and mainnet. For example with 2.2.1 we had to make a separate testnet release (2.2.1-rc.1) just to set a different voting date. With per-chain schedules we could release 2.2.1 to both mainnet and testnet.