Implement reference based transaction filter

[matiasinsaurralde]

For #55.

Still missing on this PR (it's WIP):

• P̶o̶s̶t̶g̶r̶e̶s̶ ̶s̶u̶p̶p̶o̶r̶t̶.̶ Fixed in d59c0b9
• CountTransactions fix. At the moment we count all the transactions. Could be improved as part of this PR or another one.

To test:

1. Create a transaction by using the transactions endpoint:
   URL: http://localhost:3068/quickstart/transactions
   HTTP Verb: POST
   JSON request:

{
    "reference": "myref",
    "postings": [
      {
        "source": "world",
        "destination": "central_bank",
        "asset": "GEM",
        "amount": 1000
      },
      {
        "source": "central_bank",
        "destination": "users:001",
        "asset": "GEM",
        "amount": 1000
      }
    ]
  }

2. Hit the requests endpoint adding a query parameter with the myref reference:
   URL: http://localhost:3068/quickstart/transactions?reference=myref
   HTTP Verb: GET

[codecov]

Codecov Report

Merging #60 (d43e6f5) into main (db3a32c) will decrease coverage by 0.29%.
The diff coverage is 0.00%.

❗ Current head d43e6f5 differs from pull request most recent head 7fdc146. Consider uploading reports for the commit 7fdc146 to get more accurate results

@@            Coverage Diff             @@
##             main      #60      +/-   ##
==========================================
- Coverage   34.21%   33.91%   -0.30%     
==========================================
  Files          26       26              
  Lines        1362     1374      +12     
==========================================
  Hits          466      466              
- Misses        846      857      +11     
- Partials       50       51       +1     

Impacted Files	Coverage Δ
api/http.go	0.00% <0.00%> (ø)
ledger/query/query.go	60.00% <0.00%> (-5.63%)	⬇️
storage/postgres/transactions.go	0.00% <0.00%> (ø)
storage/sqlite/transactions.go	82.96% <0.00%> (-2.54%)	⬇️

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[matiasinsaurralde]

Fixed PostgreSQL support in d59c0b9 👍