DnfContext: add dnf_context_module_install()

[jlebon]

This is a C-compatible API similar to dnf_context_module_enable()
which additionally marks the target packages for installation. This is
similar to dnf module install.

We intend to use this in rpm-ostree as well.

Closes: #874

[jlebon]

Still learning the modular parts of the codebase and my C++ is a bit rusty, so let me know if there are better ways to do some things or bits I'm missing!

[Conan-Kudo]

@jlebon You'll also want your last commit to include changelog information, per the contribution doc: https://github.com/rpm-software-management/libdnf#contribution

[jlebon]

Updated! ⬆️

[j-mracek]

@jlebon I am sorry but it looks like that the code will not work like expected (like dnf) when module stream requested to install is not enabled. @Conan-Kudo May I ask you for a ping when modularity PR appears?

[Conan-Kudo]

Yep, certainly.

[jlebon]

@jlebon I am sorry but it looks like that the code will not work like expected (like dnf) when module stream requested to install is not enabled.

Thanks for the feedback. Can you expand on the differences between the two? From my understanding, doing dnf module install on a stream which is not already enabled will also enable it. This is also doing that here the same way dnf_context_module_enable does it, no? (I.e. via modify_module_dict_and_enable_stream).