pmb.config: add the full hexdump to the list of installed build packages

This works around pmaports#3268 (closed), by always installing hexdump when building packages. The full hexdump is small (like 80KB), and even though this isn't required in most situations it seems like the best of a group of bad workarounds, until upstream/busybox fix the bug in the pmaports issue.

pmb/config/__init__.py

@@ -211,6 +211,10 @@ chroot_outdated = 3600 * 24 * 2
 # for the first time
 # IMPORTANT: the order here matters, it is the order these packages will
 # be built in (if needed). abuild must be first!
+#
+# NOTE: full hexdump is installed to workaround a bug in busybox,
+# see https://gitlab.postmarketos.org/postmarketOS/pmaports/-/issues/3268. This can be
+# reverted when the bug is properly fixed.
 build_packages = ["abuild", "apk-tools", "build-base", "ccache", "git", "hexdump"]
 
 #