Implement GetCapabilities endpoint in OpenAPI spec

[vsmalladi]

Added capabilities endpoint to retrieve TES backend features. Closes #206
Closes #188

[vsmalladi]

Response would be like this

{
  "cpu_cores": 32,
  "ram_gb": 256,
  "disk_gb": 2000,
  "num_machines": 8,
  "accelerators": [
    {
      "type": "GPU",
      "count": 4
    },
    {
      "type": "TPU",
      "count": 2
    }
  ],
  "chip_type": "x86_64",
  "fpga": true
}

[vsmalladi]

Add docker or other container resources.