SQLModel support

[bogdandm]

Add code generator for https://sqlmodel.tiangolo.com/

[bogdandm]

Fixes #49

[bogdandm]

- id: 1
  name: Mario
  secret_name: Foo
  age: 31

- id: 2
  name: Zeus
  secret_name: Bar

r"""
generated by json2python-models v0.2.7 at Mon Jan  2 16:02:11 2023
command: /opt/projects/json2python-models/json_to_models/__main__.py -s flat --max-strings-literals 0 -m Hero temp.yaml -f sqlmodel -i yaml
"""
from sqlmodel import Field, SQLModel
from typing import Optional


# Warn! This generated code does not respect SQLModel Relationship and foreign_key, please add them manually.
class Hero(SQLModel, table=True):
    id: int = Field(..., primary_key=True)
    name: str
    secret_name: str
    age: Optional[int] = None

[coveralls]

Coverage: 98.072% (+0.03%) from 98.043% when pulling c7664ef on sqlmodel-support into cdd4413 on master.