I cannot find a centralized and straightforward way of knowing what are the properties I need to set in order to achieve what I want to do. Where is that documented?
It doesn't exist.
There is a document that lists (or at least tries to) all of the common Spring properties:
However, it doesn't claim to be comprehensive. And it certainly doesn't give you a "straightforward way of knowing" what is needed for any given Spring application.
There is more specific Spring documentation on (for example) how to configure datasources. But even that is unlikely to give you a simple recipe for every application scenario.
I'm new to Spring Boot, and it's not clear to me how I can know in advance what are the Spring Boot properties I need to set up.
In general (i.e. for all possible projects), you can't know that in advance. Even if you are an Spring Boot expert. Even if you have read all of the Spring documentation. Because there will always be cases where someone has forgotten to document something, or the documentation is inadequate ... for that particular case.
In short, you need to read and (try to) understand the documentation that is available, then give it a try. And if that doesn't work, diagnose, search, read some more, ask questions ...