If container bootstrapping fails, Dangerzone GUI should inform user

[rocodes]

Context: 0.7.0-2 testing
Environment: fedora 39 (VMs)

I installed Dangerzone in a VM that was low on disk space (not on purpose! but hey), and the container was too large to download [edit: looks like /var/tmp is too small moreso than the entire disk]. I would not expect to see the "Convert documents" screen in this scenario, but I did. (Of course, conversion fails, but it would be nice to tell the user sooner before they attempt to convert documents).

(Low-priority, bug, ux, qa)

[DEBUG] Inferred system color scheme as OSColorMode.LIGHT
[DEBUG] Setting up Dangerzone updater
[DEBUG] Consulting updater settings before checking for updates
[DEBUG] Checking platform type
[DEBUG] Running on Linux, disabling updates
[DEBUG] Will not check for updates, based on updater settings
[INFO] Installing Dangerzone container image...
Getting image source signatures
Copying blob abc7eac22d8a [==============>-----] 899.6MiB / 1.2GiB | 340.1 MiB/s
Copying blob 94e5f06ff8e3 skipped: already exists  
Copying blob 4f485b582a13 done   | 
Copying blob 7c94abf90cef skipped: already exists  
Copying blob dbbcc85c9d2a skipped: already exists  
Copying blob 2ff956e302c1 skipped: already exists  
Copying blob 14cc7f665495 skipped: already exists  
Copying blob 75aecdb6c123 done   | 
Error: payload does not match any of the supported image formats:
 * oci: open /var/tmp/podman1170243093/index.json: not a directory
 * oci-archive: creating temp directory: untarring file "/var/tmp/container_images_oci900934569": write /var/tmp/container_images_oci900934569/a87ba73089224c626a1ae9bb60253406dff233a944fecaba970a670d799eb6cd/layer.tar: no space left on device
 * docker-archive: writing blob: storing blob to file "/var/tmp/container_images_storage3120192689/1": write /var/tmp/container_images_storage3120192689/1: no space left on device
 * dir: open /var/tmp/podman1170243093/manifest.json: not a directory
[ERROR] Failed to install the container image
[INFO] Assigning ID 'XxJYRZ' to doc '/home/user/Downloads/Untitled.jpg'
[DEBUG] Removing all documents
[DEBUG] Marking doc XxJYRZ as 'converting'
[INFO] > /usr/bin/podman run --log-driver none --security-opt no-new-privileges --cap-drop all --cap-add SYS_CHROOT --security-opt label=type:container_engine_t --network=none -u dangerzone --rm -i --name dangerzone-doc-to-pixels-XxJYRZ --userns nomap dangerzone.rocks/dangerzone /usr/bin/python3 -m dangerzone.conversion.doc_to_pixels
[ERROR] [doc XxJYRZ] 0% Unknown error code '125'
[DEBUG] Marking doc XxJYRZ as 'failed'

[apyrgio]

Sigh, we were aware of this issue for a long time, but we have never prioritized it (see #193).

I have added the original issue in the 0.8.0 milestone, and I'll close this one as a duplicate, so that we can track stuff in a single place. Thanks a lot for the report!