feat: add pallets/on-going-referenda endpoint

[Imod7]

Description

Closes #1431

This PR adds the pallets/on-going-referenda endpoint which returns a list of all on-going referenda and their associated info.

Query Params

• at: Which block to query, it will default to the latest finalized block. Accepts a hash or blocknumber

Sample Response

Sidecar request while connected to Kusama chain :

http://127.0.0.1:8080/pallets/on-going-referenda?at=22652724

returns

{
  "at": {
    "hash": "0xb57617ca12ccf589b0c5e1d34489198ceca6aa4f99ad0aef41f3b364baeb29a7",
    "height": "22652724"
  },
  "referenda": [
    {
      "id": "372",
      "decisionDeposit": {
        "who": "D9qBj8WnniECUWJxtbsu6ncUN24gKSi3KKp5ZPJjfG2GmaM",
        "amount": "333333333330000"
      },
      "enactment": {
        "after": "100"
      },
      "submitted": "22580366",
      "deciding": {
        "since": "22587442",
        "confirming": null
      }
    },
    {
      "id": "368",
      ...
      ...
    },
    {
      "id": "374",
      ...
      ...
      }
    },
    {
      "id": "375",
      ...
      ...
      }
    },
    {
      "id": "371",
      ...
      ...
      }
    },
    {
      "id": "370",
      ...
      ...
      }
    },
    {
      "id": "373",
      "decisionDeposit": {
        "who": "D9qBj8WnniECUWJxtbsu6ncUN24gKSi3KKp5ZPJjfG2GmaM",
        "amount": "333333333330000"
      },
      "enactment": {
        "at": "22790000"
      },
      "submitted": "22580499",
      "deciding": {
        "since": "22587439",
        "confirming": null
      }
    }
  ]
}

Then we can check the referendum id 373 in Polkassembly and can verify that it corresponds to a runtime upgrade: "#373 Upgrade Kusama v1.2.0". To streamline the process and avoid extra checks, we can directly run only this script. The script queries both Sidecar's on-going-referenda endpoint and Polkassembly API and tells us which referendum is a runtime upgrade.

Example Use

An example use of this endpoint can be found in this script runtime-upgrades-checker.

Todos

• Update docs
• Add test when call api.query.referenda is not available and throws an error
• Add test when call api.query.referenda is available and returns a list of referenda

[filvecchiato]

Looking good! Nice work!

One minor thing in the pallet service where I left the comment. I think once that is resolved it can get merged!

[TarikGul]

Great Job overall looks good, just one little nit.

[filvecchiato]

All looking good! Nice work, not sure if you want to integrate my last comment