This change allows INI config sections like
[Tracker_$idSite] to be added which will override some Tracker config for individual sites. Config that should be applied overall (or in places where we don't know what the idSite is), cannot be overridden.
@diosmosis added https://matomo.org/faq/how-to/how-do-i-configure-a-config-setting-in-the-config-ini-php-differently-for-a-specific-site/ and also added the logic for 3 more settings where this may be quite useful. Once tests pass it should be good to merge.
@diosmosis a few tests seem to need fixing and then should be good to merge