Make POST requests for decoder/encoder

[IlinValery]

• [x] Encoder endpoint:

  URL: /api/encode
  Method: POST
  Body:
  {
  "image": "binaty image",
  "key": "str",
  "text": "str"
  }
  Response (200):
  {
  "image": "binary image in bpm format"
  }

• [x] Decoder endpoint:

  URL: /api/decode
  Method: POST
  Body:
  {
  "image": "binaty image",
  "key": "str"
  }
  Response (200):
  {
  "text": "str"
  }