Provide a way to handle (internal) breaking changes

[Geod24]

Now that MainNet is deployed, we loose the ability to reset the database at will as we did for TestNet.

This means that the following will have to be handled carefully:

Database

• Change to a field's type
• Addition of new keys
• Addition of new record derived from blocks
• Removals are fine (because it just means unused data)

API

• Addition of required fields to existing endpoint (we can use json:omitempty for optional fields)
• Change to existing URLs
• Additions of new endpoints are generally okay

Consensus

I think in this area, we are still okay as the network is closed.

Sync

Since the watcher node is going to be used by exchanges, we should treat it as we treat the API.

I suggest we add a Breaking label for any breaking change, and consider its inclusion carefully.

[Geod24]

Addition of required fields to existing endpoint (we can use json:omitempty for optional fields)

Actually that is not true at the moment. The hash depends on the internal data structure, which means that even optional fields will break compatibility.