Stop using `strongestLocus2Gene` in FE queries

[d0choa]

Once https://github.com/opentargets/platform-api/pull/234 is merged in the API, the column strongestLocus2Gene will disappear. This will break all widgets (credible set) currently querying this data.

We discussed how to replace this functionality using the first element of the list of the new column l2Gpredictions #3601

[d0choa]

As reported by @jdhayhurst, we can now get the top L2G with the API using:

query q{
  gwasStudy(studyId: "GCST90002316") {
    studyId
    credibleSetCount
    credibleSets {
      studyLocusId
      l2Gpredictions(size: 1) {
        target{
          id
        }
        score
      }
    }
  }
}

Truncated response:

{
  "data": {
    "gwasStudy": [
      {
        "studyId": "GCST90002316",
        "credibleSetCount": 1046,
        "credibleSets": [
          {
            "studyLocusId": "4f0cf115c50fa961d665153b2213fb1e",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000276234"
                },
                "score": 0.9335464522426875
              }
            ]
          },
          {
            "studyLocusId": "b8f16e447d8b700d555533ba40d8253f",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000139269"
                },
                "score": 0.4840234596731199
              }
            ]
          },
          {
            "studyLocusId": "332df99e1cf7637187fc4ef97c043cf3",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000155849"
                },
                "score": 0.9521211835382799
              }
            ]
          },
          {
            "studyLocusId": "01b6e3cf3d1f57791d076798e58d5c2e",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000117598"
                },
                "score": 0.510808990505023
              }
            ]
          },
          {
            "studyLocusId": "06f82d8b34684e24c69d5261bae9103f",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000134853"
                },
                "score": 0.9939252357530146
              }
            ]
          },
          {
            "studyLocusId": "612a503ceeff71d4b49a6dbd5c31009a",
            "l2Gpredictions": [
              {
                "target": {
                  "id": "ENSG00000171988"
                },
                "score": 0.7506523714639587
              }
            ]
          },

[d0choa]

As reported by @prashantuniyal02 this is already making the credible set widgets disappear: https://ot-platform-partner.netlify.app/variant/12_6333477_C_T