Add YAML support for params

[dapplion]

JSON is a subset of YAML, so switching to a YAML parser allows consumers to choose between specifying the params as JSON or YAML.

A nice side-effect is that the README example with comments is usable as is.

I've tested a local build with both .yaml and .json and both work file.

• .yaml test: README example as is
• .json test: see below

{
  "participants": [
    {
      "elType": "geth",
      "elImage": "",
      "elLogLevel": "",
      "elExtraParams": [],
      "clType": "lighthouse",
      "clImage": "",
      "clLogLevel": "",
      "beaconExtraParams": [],
      "validatorExtraParams": []
    }
  ],

  "network": {
    "networkId": "3151908",
    "depositContractAddress": "0x4242424242424242424242424242424242424242",
    "secondsPerSlot": 12,
    "slotsPerEpoch": 32,
    "altairForkEpoch": 1,
    "mergeForkEpoch": 2,
    "totalTerminalDifficulty": 100000000,
    "numValidatorKeysPerNode": 64,
    "preregisteredValidatorKeysMnemonic": "giant issue aisle success illegal bike spike question tent bar rely arctic volcano long crawl hungry vocal artwork sniff fantasy very lucky have athlete"
  },
  "waitForMining": true,
  "waitForFinalization": false,
  "waitForVerifications": false,
  "verificationsTTDEpochLimit": 5,
  "verificationsEpochLimit": 5,
  "logLevel": "infoLLLOLLOL-JSON"
}