Feature: #82419 - Send Frontend Debug Information as HTTP Response Header

See forge#82419

Description

When setting config.debug=1 or $TYPO3_CONF_VARS[FE][debug] the parse time is now sent as HTTP response header "X-TYPO3-Parsetime" instead of HTML comments.

Impact

This ensures that non-HTML-content (e.g. JSON output) does not break when having debugging for the Frontend enabled.

If you look for the parse time of a frontend request, this can now easily be shown via curl -I https://mydomain.com or in the developer toolbar of the browser.