Include pool shares in account response

[tamirms]

Horizon already provides an endpoint to query account details. This endpoint will be modified in the case that the account is an LP for a liquidity pool. We will add an extra balance object in the response to describe how many shares of the liquidity pool are held by the account.

In the account response there is a balances field which consists of a list of balance objects. We will introduce the following breaking changes on the balance object which is included in the balances list:

• asset_type can be liquidity_pool_shares. Previously the asset_type field was restricted to: native, credit_alphanum4, or credit_alphanum12.
• buying_liabilities, selling_liabilities, asset_code, and asset_issuer are removed from the response for pool shares because they are not relevant to liquidity pools.

{
  "id": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
  "account_id": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
  "sequence": "24739097524306468",
  "subentry_count": 3,
  "inflation_destination": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
  "last_modified_ledger": 23569316,
  "num_sponsoring": 0,
  "num_sponsored": 0,
  "thresholds": {
    "low_threshold": 5,
    "med_threshold": 0,
    "high_threshold": 0
  },
  "flags": {
    "auth_required": false,
    "auth_revocable": true,
    "auth_immutable": false,
    "auth_clawback_enabled": true
  },
  "balances": [
    {
      "balance": "1.0000005",
      "limit": "922337203685.4775807",
      "buying_liabilities": "0.0000000",
      "selling_liabilities": "0.0000000",
      "last_modified_ledger": 22651481,
      "is_authorized": true,
      "is_clawback_enabled": false,
      "asset_type": "credit_alphanum4",
      "asset_code": "EURT",
      "asset_issuer": "GAP5LETOV6YIE62YAM56STDANPRDO7ZFDBGSNHJQIYGGKSMOZAHOOS2S"
    },
    {
      "balance": "0.0000000",
      "limit": "922337203685.4775807",
      "buying_liabilities": "0.0000000",
      "selling_liabilities": "0.0000000",
      "last_modified_ledger": 7877447,
      "is_authorized": false,
      "is_clawback_enabled": false,
      "asset_type": "credit_alphanum4",
      "asset_code": "PHP",
      "asset_issuer": "GBUQWP3BOUZX34TOND2QV7QQ7K7VJTG6VSE7WMLBTMDJLLAW7YKGU6EP"
    },
    {
      "liquidity_pool_id": "abcdef",
      "asset_type": "liquidity_pool_shares",
      "balance": "10",
      "limit": "10000",
      "last_modified_ledger": 7877447,
      "is_authorized": false,
      "is_clawback_enabled": false
    }
  ],
  "signers": [
    {
      "weight": 10,
      "key": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
      "type": "ed25519_public_key"
    }
  ],
}

We also want to add an endpoint to get accounts by a given liquidity pool.

GET /accounts?liquidity_pool=abcdef

Horizon already provides an endpoint to query accounts by one of three filters: signer, asset, or sponsor. We will add another filter, liquidity_pool, which will return all accounts who have a trustline for the given pool.

[
  {
    "id": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
    "account_id": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
    "sequence": "24739097524306468",
    "subentry_count": 3,
    "inflation_destination": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
    "last_modified_ledger": 23569316,
    "num_sponsoring": 0,
    "num_sponsored": 0,
    "thresholds": {
      "low_threshold": 5,
      "med_threshold": 0,
      "high_threshold": 0
    },
    "flags": {
      "auth_required": false,
      "auth_revocable": true,
      "auth_immutable": false,
      "auth_clawback_enabled": true
    },
    "balances": [
      {
        "balance": "1.0000005",
        "limit": "922337203685.4775807",
        "buying_liabilities": "0.0000000",
        "selling_liabilities": "0.0000000",
        "last_modified_ledger": 22651481,
        "is_authorized": true,
        "is_clawback_enabled": false,
        "asset_type": "credit_alphanum4",
        "asset_code": "EURT",
        "asset_issuer": "GAP5LETOV6YIE62YAM56STDANPRDO7ZFDBGSNHJQIYGGKSMOZAHOOS2S"
      },
      {
        "balance": "0.0000000",
        "limit": "922337203685.4775807",
        "buying_liabilities": "0.0000000",
        "selling_liabilities": "0.0000000",
        "last_modified_ledger": 7877447,
        "is_authorized": false,
        "is_clawback_enabled": false,
        "asset_type": "credit_alphanum4",
        "asset_code": "PHP",
        "asset_issuer": "GBUQWP3BOUZX34TOND2QV7QQ7K7VJTG6VSE7WMLBTMDJLLAW7YKGU6EP"
      },
      {
        "liquidity_pool_id": "abcdef",
        "asset_type": "liquidity_pool_shares",
        "balance": "10",
        "limit": "10000",
        "last_modified_ledger": 7877447,
        "is_authorized": false,
        "is_clawback_enabled": false
      }
    ],
    "signers": [
      {
        "weight": 10,
        "key": "GDI73WJ4SX7LOG3XZDJC3KCK6ED6E5NBYK2JUBQSPBCNNWEG3ZN7T75U",
        "type": "ed25519_public_key"
      }
    ]
  }
]

More details about this feature can be found in https://docs.google.com/document/d/1pXL8kr1a2vfYSap9T67R-g72B_WWbaE1YsLMa04OgoU/edit#