ENSv2: Index ENSv1 `manager` from ENS Registry

[shrugs]

• index the ENS Registry's owner as an ENSv1Domain's manager, including ensureAccount
• nullable and interpret zeroAddress as null
• surface via ENSv1Domain.manager -> Account

[lightwalker-eth]

@shrugs What do you think about naming this field something such as rootRegistryOwner instead of manager?

For background:

• I'm not a fan of the "owner" vs "manager" terminology that's currently in the UI of the ENSv1 Manager App. I find it to be an unfortunate obfuscation of what's actually going on that confuses both regular non-technical people and developers.
• As alternative terminology, I've been suggesting the use of tokenOwner vs rootRegistryOwner to Lev which you can find in task-for-agent.md in update API design  sevenzing/ens-relations-api#1
  • The reason I prefer this terminology is because it removes obfuscation about what is actually being owned. I believe this is quite helpful for devs and for semi-technical people it at least helps to build a more productive mental model for them about what's going on (no doubt there's no terminology that will will make this completely intuitive for all audiences without additional supporting docs).
• The existing owner field in the new GraphQL API might also be renamed to tokenOwner to help distinguish it from rootRegistryOwner.

Please critique everything here appreciate your advice.