daemon: Add zstd support to guestfs_file_architecture

This is required so we can determine the file architecture of
zstd-compressed Linux kernel modules as used by OpenSUSE and maybe
other distros in future.

Note that zstd becomes a required package, but it is widely available
in current Linux distros.

The package names come from https://pkgs.org/download/zstd and my own
research.

generator/actions_core.ml

@@ -9417,6 +9417,8 @@ with large files, such as the resulting squashfs will be over 3GB big." };
         [["file_architecture"; "/bin-x86_64-dynamic.gz"]], "x86_64"), [];
       InitISOFS, Always, TestResultString (
         [["file_architecture"; "/lib-i586.so.xz"]], "i386"), [];
+      InitISOFS, Always, TestResultString (
+        [["file_architecture"; "/lib-i586.so.zst"]], "i386"), [];
     ];
     shortdesc = "detect the architecture of a binary file";
     longdesc = "\