Please add custom_properties support similar to simplestreams-sync

Hi,

This one is a typical example of lack of consistency.
You have 3 charms here dealing with images in Glance :
* glance charm itself
* glance-simplestreams-sync
* octavia-diskimage-retrofit

These 3 charms have their own sets of options regarding image properties/conversion and there is no way to have a consistent behavior.

1) with glance, there is a "image-conversion" option in order to force conversion to raw format that is apparently doing its job *but only when the image is uploaded through CLI or Horizon dashboard* ! Images uploaded by glance-simplestreams-sync or octavia-diskimage-retrofit are *not* converted as if they can bypass this option (which is configured at the glance level so I don't even know how they can do that).

2) glance charm has no option to configure custom image properties (such as hw properties for virtio drivers, qemu-guest-agent support, ...). This is something that is supported by glance through the image property injection plugin (image_import_plugins ) which basically relies on the same principles as image conversion plugin (where we do have a charm option available). So custom properties has to be set afterwards which can easily be done with a controlled process (pipelines, whatever ...) but in some situations (where a user can upload his own custom image), we could be in some corner case where some instances could be spawned without the properties we need.

3) glance-simplestreams-sync on the other hand *has* options to set custom properties for images *but* ... no option to do image conversion, files are uploaded as qcow which is not efficient when used with a ceph storage backend for example.

4) octavia-diskimage-retrofit has no option for both custom properties and conversion ... even though the retrofit process is based on the images uploaded by glance-simplestreams-sync (which have their own set of custom properties but those properties are not inherited by the retrofited image).

This is pure mess, can't we just have options to add default custom properties and do image conversion at the glance level and have every other "image uploader" charms such as glance-simplestreams-sync and octavia-diskimage-retrofit just comply to these rules by not doing things their own way ?
Or maybe have some hierarchical layering with image uploading charms to override or add their own options on top of what is defined at the glance level but without bypassing them ?

The current situation is just illogical and inconsistent.

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/charm-glance/+/875797

Reviewed: https://review.opendev.org/c/openstack/charm-glance/+/875797
Committed: https://opendev.org/openstack/charm-glance/commit/0a1d645000576e5ccbc723614e0610eeffd29935
Submitter: "Zuul (22348)"
Branch: master

commit 0a1d645000576e5ccbc723614e0610eeffd29935
Author: Rafael Lopez <email address hidden>
Date: Wed Mar 1 01:32:01 2023 +0000

    Add configuration option for custom image properties

    Added configuration for injecting default image properties using the
    interoperable image import process. This change adds 1 configuration
    option to the charm:
    - 'custom-import-properties' to specify the desired custom properties

    Note: current glance docs example shows incorrect quoting, the
    implemented format in this change (no quotes) is correct. Docs fix
    in: https://review.opendev.org/c/openstack/glance/+/890423

    Release note: https://review.opendev.org/c/openstack/charm-guide/+/891010

    Closes-Bug: 1994053
    Related-Bug: 2028895
    Change-Id: I9548c90e663285c6e7a70eebc8c135a5568974bc

Reviewed: https://review.opendev.org/c/openstack/charm-guide/+/891010
Committed: https://opendev.org/openstack/charm-guide/commit/3b32a4af1d0205bceb54330de2b727d6f57205b3
Submitter: "Zuul (22348)"
Branch: master

commit 3b32a4af1d0205bceb54330de2b727d6f57205b3
Author: Rafael Lopez <email address hidden>
Date: Thu Aug 10 04:33:00 2023 +0000

    Add note for glance custom-image-properties

    Document new config option 'custom-image-properties' for glance
    introduced by:

    https://review.opendev.org/c/openstack/charm-glance/+/875797

    Closes-Bug: #1994053
    Change-Id: I706f9ad162a06e577af53f7c694b1d97a1d399b0

Fix proposed to branch: stable/zed
Review: https://review.opendev.org/c/openstack/charm-glance/+/897451

Fix proposed to branch: stable/yoga
Review: https://review.opendev.org/c/openstack/charm-glance/+/897504

Fix proposed to branch: stable/2023.1
Review: https://review.opendev.org/c/openstack/charm-glance/+/898078