Take length from MinLenght, MaxLength data annotation attributes to add minLength, maxLength to schema

[georgievaja]

STEPS TO REPRODUCE:

• when using MinLenght ro MaxLenght DataAnnotation attributes, no minLenght or maxLenght schema properties are being generated

EXPECTED RESULT:

• minLenght, maxLenght are in schema

ADDITIONAL DETAILS

• it would be enough if you would add

                if (attribute is MaxLengthAttribute maxLength)
                {
                    schema.maxLength = maxLength.Length;
                }

                if (attribute is MinLengthAttribute minLength)
                {
                    schema.minLength = minLength.Length;
                }

to your Swashbuckle.Core/Swagger/SchemaExtensions.cs - WithValidationProperties
but you would have to update .NET framework to 4.5 as in this pr: #1302