Add some error types in ledger package and respond with 4xx status on transaction endpoint.

[gfyrag]

No description provided.

[codecov]

Codecov Report

Merging #128 (61d2ec5) into main (4a337a9) will decrease coverage by 0.46%.
The diff coverage is 18.91%.

@@            Coverage Diff             @@
##             main     #128      +/-   ##
==========================================
- Coverage   69.75%   69.29%   -0.47%     
==========================================
  Files          68       69       +1     
  Lines        2255     2273      +18     
==========================================
+ Hits         1573     1575       +2     
- Misses        565      580      +15     
- Partials      117      118       +1     

Impacted Files	Coverage Δ
pkg/api/controllers/transaction_controller.go	10.52% <0.00%> (-1.02%)	⬇️
pkg/ledger/ledger.go	74.28% <28.57%> (-1.61%)	⬇️
pkg/ledger/error.go	55.55% <55.55%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d79996c...61d2ec5. Read the comment docs.