GraphqlV2: return hosts as Host and not as Organization

[znarf]

• Make Hosts returned as Host instead of Organization

Replace (BREAKING CHANGE):

... on Organization {
  host {
    id
    hostFeePercent
  }
}

with simpler:

... on Host {
  id
  hostFeePercent
}

or:

... on Host {
  host {
    id
    hostFeePercent
  }
}

• Make Hosts be an AccountWithHost to simplify things on the frontend side

Idea is to avoid such weird code:

... on AccountWithHost {
  host {
    id
    slug
    paypalClientId
    supportedPaymentMethods
  }
}
... on Organization {
  host {
    id
    slug
    paypalClientId
    supportedPaymentMethods
  }
}

And replace with just:

... on AccountWithHost {
  host {
    id
    slug
    paypalClientId
    supportedPaymentMethods
  }
}

[znarf]

This is a breaking change and Frontend (at least) needs to be pushed at the same time.
opencollective/opencollective-frontend#9769