Validators in forms should pull from constants in their associated models

[brassy-endomorph]

Is your feature request related to a problem? Please describe.

If there is a field that has a min or max size in a database model, there will be HTML forms that modify this field. A constant in the model should be used for both the SQLAlchemy column and the WTForm's validator.

For example, this display name field already has gotten out of sync (field size of 80 in the model, 100 in the form).

hushline/hushline/model.py

Lines 31 to 36 in bf3124b

	class User(Model):
	__tablename__ = "users"
	id: Mapped[int] = mapped_column(primary_key=True)
	primary_username: Mapped[str] = mapped_column(db.String(80), unique=True)
	display_name: Mapped[Optional[str]] = mapped_column(db.String(80))

hushline/hushline/settings.py

Lines 139 to 140 in bf3124b

	class DisplayNameForm(FlaskForm):
	display_name = StringField("Display Name", validators=[Length(max=100)])

Describe the solution you'd like

class MyModel(Model):
    MY_FIELD_MIN = 10
    MY_FIELD_MAX = 20
    ...
    my_field: Mapped[str] = mapped_column(db.String(MY_FIELD_MAX))

class MyModelForm(FlaskForm):
    my_field = StringField("My Field", validators=[Length(MyModel.MY_FIELD_MIN, MyModel.MY_FIELD_MAX)])