API: Add `treasury-history` for caching the assets overtime

[ethedev]

Add treasury history endpoint + docs:

• https://api.yam.finance/treasury-history

{
  timestamp: TIMESTAMP,
  values: {
    assets: {
      "DPI": 154057.42,
      "GITCOIN": 44965.41,
      "INDEX": 487165.24,
      "INDEXLP": 2837992.33,
      "SUSHI": 674591.54,
      "UMA": 177123.28,
      "USDC": 817.84,
      "USTONKSLP": 571104.94,
      "WETH": 804516.69,
      "YAMHOUSE": 1061100,
      "YUSD": 44265.85
    },
    total: 20000000
  }
}