[DRAFT] Introduce channel manifest when resolving feature-packs

[jfdenise]

Split the provisioning.xml content into 2 pieces:

• The provisioning.xml contains the list of known feature-packs, without versions. For backward compatibility with older Glow tooling, versions are actually kept in the file but overridden by the manifest.
• A manifest per execution context and preview/not preview is introduced to resolve feature-pack versions from the manifest.
• The manifest requires the WildFly manifest
• The manifest contains streams for the other feature-packs that don't have published manifests.
• When the other feature-packs will migrate to published manifests, streams will get removed.