Subgraph-based subgraphs scaffolding

[YaroShkvorets]

@incrypto32 We've merged in #1754 last month prior to init refactor to prevent it from going stale, but it wasn't fully working for graph init back then and doesn't work now.

This is the error that you get:

✔ Network · Ethereum Mainnet · mainnet · https://etherscan.io
✔ Source · Subgraph
✔ Subgraph slug · asdf
✔ Directory to create the subgraph in · asdf
✔ Source subgraph deployment ID · QmQfvGfWXh4pxuSykgHUJ8az26xYbxQVrRPso7MADRyuLk
✔ IPFS node to use for fetching subgraph manifest · https://api.thegraph.com/ipfs/api/v0
✔ Start block · 0
  Generate subgraph
✖ Failed to create subgraph scaffold: Cannot read properties of undefined (reading 'length')
    TypeError: Cannot read properties of undefined (reading 'length')

Could you have a look at it and finish it up?