Add a field linking to origin's web-representation of the object

Add a field with a URL linking to the origin's web-representation of the object, for each object type. This allows a smoother transition for the UI.

E.g. as we're replacing the current Kernel CI dashboard with the one using KCIDB database, we could keep linking to the old UI this way, which would have more features/data. Similarly, as we're working on integrating reporting features and data of other CI systems, we can keep linking to the original UIs to keep their data accessible.

The issue names no files or tests. Begin by locating the object-type definitions in the Python library and checking how fields are represented across them; done means each object type exposes a URL for the origin's web representation, with coverage for the existing CI origins described in the issue.

Written by the indexing model from the issue text.