Packager v3: Extend configurations to allow stream renaming

[sgallagher]

It would be useful to add an optional stream: key to the data.configurations section of the Packager v3 format. This would allow us to submit the module with a custom stream name for certain contexts.

As a real-world example, I currently maintain a variant of the 16 stream for EPEL 9 called 16-epel which is needed because the RHEL module does not provide v8-devel, needed for some EPEL packages. Right now, I have to maintain a completely separate branch in dist-git, despite the modulemd being essentially identical except for the stream name. It would be much more convenient to have an override in the configurations section instead.

[ppisar]

In other words you want to build multiple streams from a YAML file stored in a single dist-git branch.

While technically possible, there are two issues with it:

• One would need to change MBS. MBS is effectively in a maintenance mode. People who maintain it have no capacity for adding new features.
• Fedora policies require defining a stream value by a dist-git branch name https://docs.fedoraproject.org/en-US/modularity/policies/packaging-guidelines/.

[sgallagher]

1. MBS already supports doing this for the stream, since in RHEL we set the stream name because it comes from a differently-named branch. It would be fairly easy to add this to the ModulemdPackagerV3.convert_to_index() function.

2. The Fedora policies can be updated once new functionality is added.

[ppisar]

I'm not sure that MBS processes a stream value only after converting modulemd-packager into modulemd. When I wanted to add a similar feature for overriding component refs by context, I found out that MBS processes refs before the conversion.

I do not want to add yet another feature into libmodulemd which will be kept unimplemented by MBS. Like default profiles.