Add a swagger ui page for chain index endpoints

[kk-hainq]

This is a step forward for #129.

I have two questions:

1. Should we derive OpenApi.ToSchema instances with the newtype strategy like the following?
   https://github.com/input-output-hk/plutus-apps/blob/7333e3c3ae62c955c5db7799dbf1c1f58593325d/plutus-ledger/src/Ledger/Orphans.hs#L89

It is cleaner but will lead to imprecise schemas. For instance, the above Slot is returned with getSlot in the tip endpoint.

$ curl -s localhost:9083/tip | jq
{
  "tipBlockId": "fd42a734b285b01d40a90a042a92915c931458c24051e2c7e02de505dcf44ccb",
  "tipSlot": {
    "getSlot": 1714
  },
  "tipBlockNo": 684,
  "tag": "Tip"
}

The answer might be the other way around, to derive/write ToJSON through the newtype strategy more? Most things in Orphans are in plutus though.

2. It is not so clean responding with a tuple in these endpoints:
   https://github.com/input-output-hk/plutus-apps/blob/7333e3c3ae62c955c5db7799dbf1c1f58593325d/plutus-chain-index-core/src/Plutus/ChainIndex/Api.hs#L110-L112

Should we write a dedicated data type for each case, at least for better Aeson and OpenApi instances?

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[silky]

Hey @kk-hainq

Thanks for working on this!

Re: 1) I think it's fine to just use the newtype instances (It's not ideal, but it's what we do elsewhere)

Re: 2) I think a richer type might be nice, I agree.

[silky]

Nice, thanks @kk-hainq ! :) If you're happy with it I'll merge?

[kk-hainq]

@silky False alarm! I pushed those initial IsUtxoResponse commits to see if I missed any CI checks. I did, have fixed it and completed IsUtxoResponse similarly. The PR should be ready now.

Should I update and write more to plutus-chain-index & plutus-chain-index-core's READMEs next?

[silky]

Yes, that sounds great! Thanks so much for your work :)