Add availableFounders

[IvanIvanoff]

Changes

• Improve available_selectors in getMetric's metadata
• Add availableFounders to getMetric's metadata

{
  getMetric(metric: "social_volume_total") {
    metadata {
      availableFounders {
        name
        project {
          name
        }
      }
    }
  }
}

{
  "data": {
    "getMetric": {
      "metadata": {
        "availableFounders": [
          {
            "name": "Mingxing “Star” Xu",
            "project": {
              "name": "OKB"
            }
          },
          {
            "name": "Rune Christensen",
            "project": {
              "name": "Maker"
            }
          },
...
        ]
      }
    }
  }
}

Ticket

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have tried to find clearer solution before commenting hard-to-understand parts of code
• I have added tests that prove my fix is effective or that my feature works