GraphQL: Restructure market data object

[edd]

chore (non-blocking) In the future, let's tidy this object up so that fields that don't apply to all markets don't apply to all markets. I've marked this as non blocking as there'll almost certainly be more than just this field. I'll file a ticket.

Originally posted by @edd in https://github.com/vegaprotocol/vega/pull/9135#discussion_r1301465093

Task

• [ ] Restructure the market object to separate out the different MarketData types:
  • FuturesMarketData
  • SpotMarketData
  • PerpsMarketData
• [ ] Ensure that the types overlap where they share fields
• [ ] Scope type specific fields to the relevant type