[MM-54770] Add ability to export profile pictures and fix importing them (#25042)

* add ability to export pp and fix import

* remove unused nopSeeker

* remove debug log

* fix shadow vars

* generate a warning instead of an error when unable to export profile picture

* fix merge conflicts

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/server.go

@@ -1748,7 +1748,7 @@ func (s *Server) GetProfileImage(user *model.User) ([]byte, bool, *model.AppErro
 		return img, false, nil
 	}
 
-	path := "users/" + user.Id + "/profile.png"
+	path := getProfileImagePath(user.Id)
 
 	data, err := s.ReadFile(path)
 	if err != nil {