RFE - Support [[containers]] in blueprints to permit Microshift offline container images as part of the image

[luisarizmendi]

There is [[containers]] section in blueprints [1] that is used to include the required container images to run Microshift in a disconnected environment without any external container image registry [2].

I think it's a good idea to include a new variable to include this section in the blueprint generated by the collection if needed.

[1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html-single/composing_a_customized_rhel_system_image/index#con_the-container-image-builder-customization_assembly_pushing-a-container-to-a-register-and-embedding-it-into-a-image

[2] https://access.redhat.com/documentation/en-us/red_hat_build_of_microshift/4.14/html/installing/microshift-embed-in-rpm-ostree-for-offline-use#doc-wrapper