gitlab-ci: add 'twister-qemu-goliothd' job

[mniestroj]

This job will run all QEMU tests and samples that require network access and communication with 'goliothd'.

Add a script for configuring NAT with iptables, so that QEMU can access external world.

Use twister_report.xml instead of twister.xml, as the former shows time spent on each testcase separately and also trims down information about target platform (which is obvious based on job name).

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit f9c2fdf):

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[mniestroj]

@ncmiller Please note failure of nrf52840dk test. Merging, as it is not affected by this PR.