[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/imports/import_validators.go

@@ -190,9 +190,9 @@ func ValidateChannelImportData(data *ChannelImportData) *model.AppError {
 }
 
 func ValidateUserImportData(data *UserImportData) *model.AppError {
-	if data.ProfileImage != nil {
+	if data.ProfileImage != nil && data.ProfileImageData == nil {
 		if _, err := os.Stat(*data.ProfileImage); os.IsNotExist(err) {
-			return model.NewAppError("BulkImport", "app.import.validate_user_import_data.profile_image.error", nil, "", http.StatusBadRequest)
+			return model.NewAppError("BulkImport", "app.import.validate_user_import_data.profile_image.error", nil, "", http.StatusBadRequest).Wrap(err)
 		}
 	}