Description

I'd like to propose adding support for custom format types. These could come from the configuration. Maybe something like the following example:

generator:
  formats:
    decimal: github.com/shopspring/decimal.Decimal

This would result in a field with format: decimal to be of the type decimal.Decimal from the package github.com/shopspring/decimal.

Alternatively, we could implement this as an extension e.g.

type: string
x-ogen-type: github.com/shopspring/decimal.Decimal

We can implement some checks to ensure the package is importable, as well as checking that the type implements one of the following interfaces:

interface {
  Encode(e *jx.Encoder)
  Decode(d *jx.Decoder) error
}

interface {
  json.Marshaler
  json.Unmarshaler
}

interface {
  encoding.TextMarshaler
  encoding.TextUnmarshaler
}

Based on which of the interfaces it implements we can use a different template for encoding and decoding the value.

I'm happy to implement this feature, just wanted to first check if such a feature would be accepted and get alignment on the way it's configured.