Get a list of all custom fields by passing no Path Params. Pass the Path Param for getting particular
custom fields. Each custom field has the following keys
|Custom Field ID.
|User that is logged in.
|Name of custom field.
|Field type of the custom field.
|If field_type is Multi-choice, It is the list of choices.
|Creation date of the custom field.
|Date at which custom field is modified.