Query function: build artifact metadata

[mxmxchere]

It is planned to extend the info.yaml format in a way that it will contain a list of generated build artifacts. This information should be exposed so that it can be used by gl-oci.

[Vincinator]

Implemented get_oci_metadata function to return information required by deducing media types based on cname.

• based on cname we get the list of all features
• for each feature, we check if an image.<filetype> or convert.<filetype> file exists in that folder
• if such a file exists, we adapt layer information to have the right media type for
• if such a file does not exist, defaults of .raw and .tar mediatypes are assumed

Task is done, however, after completion of initial delivery we can talk about refactoring to a query based approach if required