.gitlab/ci/build-inside-vm.sh:
Create an ephemeral signing key for signing the rootfs image (e.g. squashfs or erofs) when building the profiles.
Implements #125
.gitlab/ci/build-host.sh:
Change the readonly TMPDIR variable to a global tmpdir variable and set it in the `init()` function.
.gitlab/ci/build-inside-vm.sh:
Change assigning the readonly tmpdir variable directly to assigning it after declaring it.
Change `cleanup()` and `create_zsync_delta()` to use bash-style statements and also check whether SUDO_GID is set before
using it.
.gitlab/ci/build-host.sh:
Add script to be run in a container with access to qemu.
It is a slight modification of arch-boxes' build-host.sh script to cater to the specific archiso requirements.
.gitlab/ci/build-inside-vm.sh:
Add script to be run in virtualized environment, established by build-host.sh.
This script builds the actual archiso profiles and creates checksum for the resulting image files.
