Add initial value to the form Field model

[quillcraftsman]

Is your feature request related to a problem? Please describe.
Frequently we use initial value in django model field. We can't test in now with Field model

Describe the solution you'd like

• Add new parameter "initial" to the Field model
• Add special assert to the TestCaseMixin
• Add condition to the main assert assertTrueFrom

Describe alternatives you've considered

Additional context
This is the form example to test initial value:

class LoadTrainingDataForm(forms.Form):
    name = forms.CharField(max_length=128, widget=forms.TextInput(attrs={
        'class': 'form-control'
    }))
    excel_file = forms.FileField(max_length=128, widget=forms.FileInput(attrs={
        'class': 'form-control'
    }))
    sheet_name = forms.IntegerField(required=False, initial=0, widget=forms.NumberInput(attrs={
        'class': 'form-control'
    }))