Fix profile image URLs for image storage on non-public S3 buckets

In image_helpers.py, the _get_profile_image_urls() method would append
"?v=<version>" to the query string for serving profile images.

This might break serving profile images if

* EDXAPP_PROFILE_IMAGE_BACKEND was configured with its class option
  set to django.storages.s3boto3.S3Boto3Storage (or its deprecated
  predecedessor, django.storages.s3boto.S3BotoStorage), and
* that backend used signed URLs with query-string authentication (i.e.
  was *not* configured with an S3 custom domain).

When both the above conditions are met, then the URL returned by the
storage backend's url() method already contains "?", and
_get_profile_image_urls() would add another. This results in a query
string that doesn't exactly violate RFC 3986, but is discouraged by
it.[1]

Amazon S3 itself may be able to parse these query strings correctly,
but other S3 API implementations (such as Ceph radosgw[2]) may not,
and the problem is easily avoided by just looking for "?" in the
rendered URL, and using "&v=<version>" instead if we find a match.

The proper way of appending the v=<version> query parameter would
probably be to pull the URL and the query string apart and then back
together[3], but that's most likely overdoing it.

[1] https://tools.ietf.org/html/rfc3986#section-3.4 says:
"However, as query components are often used to carry identifying
information in the form of "key=value" pairs and one frequently used
value is a reference to another URI, it is sometimes better for
usability to avoid percent- encoding those characters." ("Those
characters" being "/" and "?".)

[2] https://docs.ceph.com/docs/master/radosgw/s3/

[3] https://docs.python.org/3/library/urllib.parse.html

openedx/core/djangoapps/user_api/accounts/image_helpers.py

@@ -55,7 +55,12 @@ def _get_profile_image_urls(name, storage, file_extension=PROFILE_IMAGE_FILE_EXT
         url = storage.url(
             _get_profile_image_filename(name, size, file_extension=file_extension)
         )
-        return '{}?v={}'.format(url, version) if version is not None else url
+        # Return the URL, with the "v" parameter added as its query
+        # string with "?v=". If the original URL already includes a
+        # query string (such as signed S3 URLs), append to the query
+        # string with "&v=" instead.
+        separator = '&' if '?' in url else '?'
+        return '{}{}v={}'.format(url, separator, version) if version is not None else url
 
     return {size_display_name: _make_url(size) for size_display_name, size in settings.PROFILE_IMAGE_SIZES_MAP.items()}