feat: add asset-conversion endpoints

[bee344]

Closes issue #1308

Description

Adds the endpoints /pallets/asset-conversion/liquidity-pools which returns an array of the existing liquidity pool tokens, and /pallets/asset-conversion/next-available-id which returns a string of the next available liquidity pool's id.

Query Params

at: Which block to query, defaults to latest finalized block if empty. Accepts a hash or a block number.

Sample Response

While connected to Westend Assst Hub and requesting /pallets/liquidity-pools, the return result is/should be simmilar to the following :

{
   "at":{
      "hash":"0xd712c01e62c4ec702c4b56e01cbbfd1b20e9008b18f4ebee6b1d854e26a8fd82",
      "height":"91"
   },
   "pools":[
      {
         "reserves":[
            {
               "parents":"1",
               "interior":{
                  "here":null
               }
            },
            {
               "parents":"0",
               "interior":{
                  "x2":[
                     {
                        "palletInstance":"50"
                     },
                     {
                        "generalIndex":"2"
                     }
                  ]
               }
            }
         ],
         "lpToken":{
            "lpToken":"1"
         }
      },
      {
         "reserves":[
            {
               "parents":"1",
               "interior":{
                  "here":null
               }
            },
            {
               "parents":"0",
               "interior":{
                  "x2":[
                     {
                        "palletInstance":"50"
                     },
                     {
                        "generalIndex":"1"
                     }
                  ]
               }
            }
         ],
         "lpToken":{
            "lpToken":"0"
         }
      }
   ]
}

While connected to Westend Asset Hub and requesting /pallets/next-available-id, the return result is/should be the following :

{
   "at":{
      "hash":"0xedb8792b4cd1ed8a8d5638e2fa5c7739cb4f4d93a68b20d5facc4888d2753131",
      "height":"736"
   },
   "id":"2"
}

TODO

• Add tests

[TarikGul]

LGTM, really great job, just a few nits to resolve!

[marshacb]

Awesome PR! A very small nit/question. Once any lingering merge conflicts are handled looks good to go :)

[TarikGul]

In terms of the failing docker check in gitlab, I think its not relevant to your PR but a version of buildah.