Clarify AL2 Core and AL2 Extras Advisories

We have made enhancements to our Amazon Linux 2 (AL2) core and Amazon Linux 2 (AL2) extras advisories to further specify which repository an update applies to. Please visit this page to learn more about AL2 Extras and this FAQ section for the difference between AL2 Core and AL2 Extras advisories. Each AL2 core and extra advisory has a note to specify which repository it is applicable to.