Add an easy way to change extra = meta option

[sobolevn]

Right now all models allow extra fields:

django-ninja-jwt/ninja_jwt/schema.py

Line 100 in 2fb51bf

# extra = "allow"

I don't want that behavior, I want to be strict on my input types: no extras are allowed in authentication.
So, how to change that?

Now I have to change all settings in

NINJA_JWT = {
  'TOKEN_OBTAIN_PAIR_INPUT_SCHEMA': "custom",
  'TOKEN_OBTAIN_PAIR_REFRESH_INPUT_SCHEMA': "custom",
  'TOKEN_VERIFY_INPUT_SCHEMA': "custom",
}

To only change one configuration option.

I would like to see something like:

NINJA_JWT = {
  'SCHEMAS_EXTRA': 'forbid',  # with 'allow' as default for backward-compat
}

See https://docs.pydantic.dev/latest/api/config/#pydantic.config.ConfigDict.extra