Ask HN: Best way to create a searchable knowledge base?

Have you had the experience of using/developing knowledge bases? Here is my scenario:

My team is dealing with a lot of information: Wikis, Code repos, Monitoring dashboards, internal chat messages, emails, Task tickets, related systems, etc.

There are many cases when we need to do ad-hoc searches for anything related to a concept. For instance, imagine if someone makes a change to a metric, there is a need to find all dashboards that might be using this metric to make sure they are still valid after the change.

I don't want to just fix this problem, but create the ability to find related information in ad-hoc cases.

The ramp-up time is not important, as long as some positive value can be created with a small initial effort.

Any existing products (Paid/Free/Open Source, etc) and any references to existing knowledge (designs, discussions) about this would be really appreciated.