What is the recommended strategy for building site from multiple repositories?

[voroninp]

I am planning to document every service the system has. I want to bring all the documentation to a single repository and publish it to GitLab pages.

What is the best approach for it?

I can generate websites for each repo and push them to the docs repository, but then it's not clear how I combine it with static documentation and sites from other services.

It looks better to generate metadata and extract content, push it to the docs repository and then build a large docs site. But how can I force docfx to extract everything without building the website?