GraphQL API: project and group fields argument fullPath should be case insensitive

Summary

fullPath field in our GraphQL API should be case insensitive since our full paths are intended to be so

Steps to reproduce

Open https://gitlab.com/-/graphql-explorer Use query

{
  project(fullPath: "gitlab-org/Gitlab") {
    id
  }
  group(fullPath: "Gitlab-org"){
    id
  }
}

Expected result:

{
  "data": {
    "project": {
      "id": "gid://gitlab/Project/278964"
    },
    "group": {
      "id": "gid://gitlab/Group/9970"
    }
  }
}

Actual result:

{
  "data": {
    "project": null,
    "group": null
  }
}