[build]: Provide support for apt install packages (sonic-net#7346)

apt-package handling: These are part of the Export variables for .j2 files and is needed for Debian and its derivatives.

How I did it
Add support to slave.mk files to export APT_PACKAGES and DBG_APT_PACKAGES

How to verify it
The apt package, provides the apt management tool, a high-level command-line interface for better interactive usage. APT also includes command-line programs for dealing with packages, which use the library. Three such programs are apt, apt-get and apt-cache and can be verified for their existence.

slave.mk

@@ -746,6 +746,7 @@ $(addprefix $(TARGET_PATH)/, $(DOCKER_IMAGES)) : $(TARGET_PATH)/%.gz : .platform
 		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_pydebs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_PYTHON_DEBS)))\n" | awk '!a[$$0]++'))
 		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_whls=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_PYTHON_WHEELS)))\n" | awk '!a[$$0]++'))
 		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_dbgs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_DBG_PACKAGES)))\n" | awk '!a[$$0]++'))
+		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_pkgs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_APT_PACKAGES)))\n" | awk '!a[$$0]++'))
 		j2 $($*.gz_PATH)/Dockerfile.j2 > $($*.gz_PATH)/Dockerfile
 		# Prepare docker build info
 		PACKAGE_URL_PREFIX=$(PACKAGE_URL_PREFIX) \
@@ -797,6 +798,7 @@ $(addprefix $(TARGET_PATH)/, $(DOCKER_DBG_IMAGES)) : $(TARGET_PATH)/%-$(DBG_IMAG
 		# Export variables for j2. Use path for unique variable names, e.g. docker_orchagent_debs
 		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_dbg_debs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_DBG_DEPENDS),RDEPENDS))\n" | awk '!a[$$0]++'))
 		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_image_dbgs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_DBG_IMAGE_PACKAGES)))\n" | awk '!a[$$0]++'))
+		$(eval export $(subst -,_,$(notdir $($*.gz_PATH)))_dbg_pkgs=$(shell printf "$(subst $(SPACE),\n,$(call expand,$($*.gz_DBG_APT_PACKAGES),RDEPENDS))\n" | awk '!a[$$0]++'))
 		./build_debug_docker_j2.sh $* $(subst -,_,$(notdir $($*.gz_PATH)))_dbg_debs $(subst -,_,$(notdir $($*.gz_PATH)))_image_dbgs > $($*.gz_PATH)/Dockerfile-dbg.j2
 		j2 $($*.gz_PATH)/Dockerfile-dbg.j2 > $($*.gz_PATH)/Dockerfile-dbg
 		# Prepare docker build info