Use bytes instead of [n]bytes to represent decimal type

[lyuboxa]

Description

Since each value may have larger size, as per spec https://avro.apache.org/docs/1.10.2/spec.pdf

{
  "type": "bytes",
  "logicalType": "decimal",
  "precision": 4,
  "scale": 2
}

A decimal logical type annotates Avro bytes or fixed types. The byte array must contain the two's-complement representation of the unscaled integer value in big-endian byte order. The scale is fixed, and is specified using an attribute.

Quick checks:

• I have followed the Code Guidelines.
• There is no other pull request for the same update/change.
• I have written unit tests.
• I have made sure that the PR is of reasonable size and can be easily reviewed.

[hariso]

🚀