feat: Add subentities array support

[antiyro]

Could it be possible to add subentities array support to make this kind of schema work :

type Transaction @entity {
  # txn hash
  id: ID!
  # block txn was included in
  blockNumber: BigInt!
  # timestamp txn was confirmed
  timestamp: BigInt!
  # gas used during txn execution
  gasUsed: BigInt!
  gasPrice: BigInt!
  # derived values
  mints: [Mint]! @derivedFrom(field: "transaction")
  burns: [Burn]! @derivedFrom(field: "transaction")
  swaps: [Swap]! @derivedFrom(field: "transaction")
  flashed: [Flash]! @derivedFrom(field: "transaction")
  collects: [Collect]! @derivedFrom(field: "transaction")
}

(from uniswap-v3 subgraph))