bib: allow blueprints in toml as well

[mvo5]

This commit adds support to load blueprints from toml as well.

[draft as tests are missing]

[achilleas-k]

I expressed a preference for toml to make life easier for adding kickstart files (see osbuild/images#631). What I'd like to see, either in this PR or a follow-up:

• Automatic detection of /config.toml like we do for /config.json.
• Prioritise toml in docs (downstream docs should be aware of this too).
• Move the config one level down, so the blueprint is the top level object, just like in osbuild-composer (this is optional; might be good to have the blueprint as a second level if we want to add BIB specific config options that don't come from the osbuild-composer blueprint).

The latest one should be a followup

[henrywang]

I have one suggestion on this feature. It will be wonderful to align this toml configuration file with toml file used by osbuild-composer. So the osbuild-composer Blueprint Refreence can be re-used as a reference. Thanks!

[achilleas-k]

I have one suggestion on this feature. It will be wonderful to align this toml configuration file with toml file used by osbuild-composer. So the osbuild-composer Blueprint Refreence can be re-used as a reference. Thanks!

Since we use a very limited number of options here, it might be better to have a dedicated page for BIB. Or maybe we could add a third bubble colour for bootc-image-builder like we have for on-prem vs console.

[mvo5]

I have one suggestion on this feature. It will be wonderful to align this toml configuration file with toml file used by osbuild-composer. So the osbuild-composer Blueprint Refreence can be re-used as a reference. Thanks!

Since we use a very limited number of options here, it might be better to have a dedicated page for BIB. Or maybe we could add a third bubble colour for bootc-image-builder like we have for on-prem vs console.

I have a branch ready for this in https://github.com/osbuild/bootc-image-builder/compare/main...mvo5:use-toml-blueprints-compat?expand=1 - it also keeps the legacy format compatiblity for now

[achilleas-k]

Excellent. LGTM!