[build] use overlay2 for DinD by default (#19078)

overlay2 is more faster comparing to vfs (more info in #11111)
And we use this option to build SONiC almost two years.
But it may be not obvious for some people that default choice is slow.
I think we should set overlay2 as a default storage driver for DinD.

rules/config

@@ -306,7 +306,7 @@ INCLUDE_FIPS ?= y
 ENABLE_FIPS ?= n
 
 # SONIC_SLAVE_DOCKER_DRIVER - set the sonic slave docker storage driver
-SONIC_SLAVE_DOCKER_DRIVER ?= vfs
+SONIC_SLAVE_DOCKER_DRIVER ?= overlay2
 
 # SONIC_OS_VERSION - sonic os version
 SONIC_OS_VERSION ?= 12