CI: Integration tests, initial setup of tool chain for

As a state-aware content publisher that is interested in avoiding unintended side-effects, I need to assert presence of certain values on certain web routes, in order to be reassured about what we are publishing.

This begins with presence and content of the technical system collection, such as robots.txt and security.txt in their well-known locations, but later eventually more details

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• There is a CI pipeline which executes after each successful deployment (first to nightly and next, subsequently also to `live), which checks the generated output against predefined criteria.