use ostree commands to fetch remote URLs

[sebhoss]

Newer fedora-iot versions don't seem to include any files in /etc/ostree/remotes.d anymore, yet ostree remote list returns a list of remotes. Therefore, we are using that and its sibling ostree remote show-url to get all update URLs.

Relates to #98

Some more data here:

[root@rpi4 ~]# ls -la /etc/ostree/remotes.d/
total 8
drwxr-xr-x. 2 root root 4096 Sep 17 09:31 .
drwxr-xr-x. 3 root root 4096 Sep 17 09:31 ..

[root@rpi4 ~]# rpm-ostree status
State: idle
Deployments:
● fedora-iot:fedora/stable/aarch64/iot
                  Version: 38.20230915.0 (2023-09-15T14:10:44Z)
               BaseCommit: d71b230901de0739b05f67f13f0626dd3a2c3a3e8105cfcaf97998f5417564f9
             GPGSignature: Valid signature by 6A51BBABBA3D5467B6171221809A8D7CEB10B464
          LayeredPackages: cockpit cockpit-podman

[root@rpi4 ~]# cat /etc/os-release 
NAME="Fedora Linux"
VERSION="38.20230915.0 (IoT Edition)"
ID=fedora
VERSION_ID=38
VERSION_CODENAME=""
PLATFORM_ID="platform:f38"
PRETTY_NAME="Fedora Linux 38.20230915.0 (IoT Edition)"
ANSI_COLOR="0;38;2;60;110;180"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:38"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f38/system-administrators-guide/"
SUPPORT_URL="https://ask.fedoraproject.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=38
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=38
SUPPORT_END=2024-05-14
VARIANT="IoT Edition"
VARIANT_ID=iot
OSTREE_VERSION='38.20230915.0'

[say-paul]

fetching it from rpm-ostree directly makes sense but this action needs to iterative as rpm-ostree can have multiple remotes that it can rebase off. reference doc