base-files: sysupgrade: exclude apk files from backup

base-files: sysupgrade: exclude apk files from backup

Exclude more apk related files from the sysupgrade backup list when
using the various options that scan /etc for changes.

Ensure removal of the system generated distfeeds list, as that
contains kernel- and version-specific urls and should never be
retained.

Also exclude any '*.apk-new' files, equivalent to the old '*-opkg'
files, which may have been created during package installation.

Example before
  $ sysupgrade -l -c | grep apk
  /etc/apk/keys/buildroot.pem
  /etc/apk/repositories.d/customfeeds.list
  /etc/apk/repositories.d/distfeeds.list
  /etc/owut.d/pre-install.sh.apk-new
  /etc/config/adblock.apk-new

After
  $ sysupgrade -l -c | grep apk
  /etc/apk/keys/buildroot.pem
  /etc/apk/repositories.d/customfeeds.list

Signed-off-by: Eric Fahlgren <ericfahlgren@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22937
Signed-off-by: Robert Marko <robimarko@gmail.com>