hostapp-update-hooks: Soft include balena-config-defaults

[mtoman]

a203bcdfd567c0cc4b4ed9de493513142cd7463f introduced a dependency on /usr/sbin/balena-config-defaults to hostapp-update-hooks, however during HUP the script is not only executed in the "new" OS container but directly in the context of the "old" OS as well, so /usr/sbin/balena-config-defaults needs to exist there. The file was introduced in balenaOS v2.99.28, so trying to HUP from anything before that will fail.

This patch changes this to a soft dependency so even if the file is missing HUP will continue.

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[mtoman]

The PR is not getting updated as I push into the branch for some reason