fix SonarQube code line duplication on folder `array_element_type`

Html pages are produced in the frontend using Jinja2 features out of some base templates and macro. This approach unavoidably increase the number of line duplication in the code (as raised by SonarQube). Some further refactoring of the templates might still be possible, but the same python targets cannot be easily reached, and eventually should be revised for JS.

For the moment being we temporarily mask the array_element_type folder (which contains most of the produced template pages) to SonarQube.