apk-tools: implement compression of on-device scripts.tar

apk-tools: implement compression of on-device scripts.tar

Default behavior for apk was to create an uncompressed scripts.tar
file.  Due to the structure of tar files, with fixed block
size and null padding, this file becomes very large on OpenWrt
installations where there are typically two scripts per package.
This could cause the raw tar file to easily grow to over 500KB,
whereas the compressed file is generally around 20-30KB.

When stored in the /rom partition of a squashfs device, the file
is compressed and this is not an issue.  But, as soon as you add
or delete a package, the scripts.tar file is fully expanded into
the /overlay partition and can cause issues on small-flash devices.

This issue was addressed in an upstream commit by detecting
whether the scripts.tar file is compressed (its name must be
exactly 'scripts.tar.gz'), and then retaining that compression by
reading/writing the file using a compressed stream.

This commit applies a cherrypicked patch for the upstream commit, and
compresses the scripts.tar during construction of the device rootfs.

Fixes: https://github.com/openwrt/openwrt/issues/17108
Link: https://gitlab.alpinelinux.org/alpine/apk-tools/-/commit/012cdcfdf981453b572a70c9568e8df6d0fe0ca1
Signed-off-by: Eric Fahlgren <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20795
Signed-off-by: Robert Marko <[email protected]>