Pass query params to GETs in dApp ledgerApi proxy

[alexmatson-da]

The dApp API spec provides a ledgerApi RPC method that proxies through to a ledger client. Some GET endpoints require query parameters, but we offer no way of providing them in the spec (we only provide body for POSTs in the request args)

Also, they do not get passed into the ledger client call in the dApp controller

We should also make requestMethod case in-sensitive, so that get and GET are both valid.