Added East US region to the list for mem opt premium-series HW (#35176)

Co-authored-by: learn-build-service-prod[bot] <113403604+learn-build-service-prod[bot]@users.noreply.github.com>

Author: vladai78

azure-sql/managed-instance/region-availability.md

@@ -48,6 +48,7 @@ Supports for the memory-optimized premium-series hardware and the premium-series
 - Canada Central
 - Canada East
 - Central US
+- East US
 - East US 2
 - North Central US
 - South Central US