custom_profile_fields: Add "display_in_profile_summary" field in model.

To allow `custom_profile_field` to display in user profile popover,
added new boolean field "display_in_profile_summary" in its model class.

In `custom_profile_fields.py`, functions are edited as per conditions,
like currently we can display max 2 `custom_profile_fields` except
`LONG_TEXT` and `USER` type fields.

Default external account custom profile fields made updatable for only
this new field, as previous they were not updatable.

Fixes part of: #21215

zerver/lib/types.py

@@ -29,11 +29,12 @@ RealmUserValidator = Callable[[int, object, bool], List[int]]
 ProfileDataElementValue = Union[str, List[int]]
 
 
-class ProfileDataElementBase(TypedDict):
+class ProfileDataElementBase(TypedDict, total=False):
     id: int
     name: str
     type: int
     hint: str
+    display_in_profile_summary: bool
     field_data: str
     order: int