package/Makefile & ipkg-make-index.sh: add full package data list

The external script used to generate the package lists for the
LEDE wiki's table of packages [1] and package indexes [2] requires
a "Source:" field in the package lists to find package makefiles.
The package makefiles are used to read the package's Category and Submenu.

The "Source:" field was removed in commit
b4aa3c899c
to reduce package list sizes and lessen opkg issues in low ram devices.

Add a separate package list file with full data to be used by the wiki's script.
It's called Packages.manifest and isn't compressed as it's not necessary.

1. https://lede-project.org/packages/start
2. https://lede-project.org/packages/index/start

Signed-off-by: Alberto Bursi <alberto.bursi@outlook.it>

package/Makefile

@@ -88,7 +88,8 @@ $(curdir)/index: FORCE
 	@for d in $(PACKAGE_SUBDIRS); do ( \
 		mkdir -p $$d; \
 		cd $$d || continue; \
-		$(SCRIPT_DIR)/ipkg-make-index.sh . 2>&1 > Packages && \
+		$(SCRIPT_DIR)/ipkg-make-index.sh . 2>&1 > Packages.manifest; \
+		grep -vE '^(Maintainer|LicenseFiles|Source|Require)' Packages.manifest > Packages && \
 			gzip -9nc Packages > Packages.gz; \
 	); done
 ifdef CONFIG_SIGNED_PACKAGES