Filter transactions by reference

[altitude]

Summary
We should be able to filter transactions by reference

Solution proposal

GET /:ledger/transactions?reference=1234

Expected behavior

• There should be zero or one transaction returned, if one exists with the matching reference
• Works with both SQLite and Postgres storage backends

curl -X POST -H "Content-Type: application/json" http://localhost:3068/test-01/transactions -d \
'{
   "postings": [
     {
       "source": "world",
       "destination": "test:001",
       "amount": 100,
       "asset": "USD/2"
     }
   ],
   "reference": "foobar"
 }'

curl -X GET http://localhost:3068/test-01/transactions?reference=foobar | jq .
# ^ should return the transaction