feat: add optional-exposed extra field type to registration form

This defines optional extra fields that are not hidden under the toggle on the 
registration page.

openedx/core/djangoapps/user_api/helpers.py

@@ -135,7 +135,7 @@ class FormDescription:
 
     def add_field(
             self, name, label="", field_type="text", default="",
-            placeholder="", instructions="", required=True, restrictions=None,
+            placeholder="", instructions="", exposed=None, required=True, restrictions=None,
             options=None, include_default_option=False, error_messages=None,
             supplementalLink="", supplementalText=""
     ):
@@ -159,6 +159,9 @@ class FormDescription:
             instructions (unicode): Short instructions for using the field
                 (e.g. "This is the email address you used when you registered.")
 
+            exposed (boolean): Whether the field is shown if not required.
+                If the field is not set, the field will be visible if it's required.
+
             required (boolean): Whether the field is required or optional.
 
             restrictions (dict): Validation restrictions for the field.
@@ -195,6 +198,9 @@ class FormDescription:
             )
             raise InvalidFieldError(msg)
 
+        if exposed is None:
+            exposed = required
+
         field_dict = {
             "name": name,
             "label": label,
@@ -202,6 +208,7 @@ class FormDescription:
             "defaultValue": default,
             "placeholder": placeholder,
             "instructions": instructions,
+            "exposed": exposed,
             "required": required,
             "restrictions": {},
             "errorMessages": {},
@@ -268,6 +275,7 @@ class FormDescription:
                     "label": "Cheese or Wine?",
                     "defaultValue": "cheese",
                     "type": "select",
+                    "exposed": True,
                     "required": True,
                     "placeholder": "",
                     "instructions": "",
@@ -283,6 +291,7 @@ class FormDescription:
                     "label": "comments",
                     "defaultValue": "",
                     "type": "text",
+                    "exposed": False,
                     "required": False,
                     "placeholder": "Any comments?",
                     "instructions": "Please enter additional comments here."

openedx/core/djangoapps/user_api/tests/test_helpers.py

@@ -95,6 +95,7 @@ class FormDescriptionTest(TestCase):
             placeholder="placeholder",
             instructions="instructions",
             required=True,
+            exposed=True,
             restrictions={
                 "min_length": 2,
                 "max_length": 10
@@ -110,8 +111,8 @@ class FormDescriptionTest(TestCase):
                json.dumps({'method': 'post',
                            'submit_url': '/submit',
                            'fields': [{'name': 'name', 'label': 'label', 'type': 'text', 'defaultValue': 'default',
-                                       'placeholder': 'placeholder', 'instructions': 'instructions', 'required': True,
-                                       'restrictions': {'min_length': 2, 'max_length': 10},
+                                       'placeholder': 'placeholder', 'instructions': 'instructions', 'exposed': True,
+                                       'required': True, 'restrictions': {'min_length': 2, 'max_length': 10},
                                        'errorMessages': {'required': 'You must provide a value!'},
                                        'supplementalLink': '', 'supplementalText': '',
                                        'loginIssueSupportLink': 'https://support.example.com/login-issue-help.html'}]})