[ANCHOR-809] Add funding_method to SEP-6/31 infoSchema

[JiahuiWho]

Part of ticket https://stellarorg.atlassian.net/browse/ANCHOR-809
The response should looks like:

  {
    "receive": {
      "JPYC": {
        "enabled": true,
        "quotes_supported": true,
        "quotes_required": false,
        "min_amount": 0,
        "max_amount": 1000000,
        "funding_method": ["SEPA", "SWIFT"],
        "fields": { ... }
      },
      "USDC": {
        "enabled": true,
        "quotes_supported": true,
        "quotes_required": false,
        "min_amount": 0,
        "max_amount": 10, 
        "funding_method": ["SEPA", "SWIFT"],
        "fields": { ... }
      }
    }
  }

[stellar-jenkins]

Preview is available here:
http://stellar-anchor-tests-pr164.previews.kube001.services.stellar-ops.com/

[stellar-jenkins]

Preview is available here:
http://stellar-anchor-tests-pr164.previews.kube001.services.stellar-ops.com/