Feature: #83476 - Load merged JS files asynchronous

See Issue #83476

Description

The async attribute is now assigned to the script tag of the concatenated JS files if all files have the async attribute enabled in TypoScript.

Example:

config.concatenateJs = 1

page = PAGE
page.includeJSFooter {
    test = fileadmin/user_upload/test.js
    test.async = 1

    test2 = fileadmin/user_upload/test2.js
    test2.async = 1
}