I'm guessing no, or at most just have set of extensions that you can use (kind of like it's done in AWS RDS or AWS Aurora). The claim is "serverless" i.e. you

I'm guessing no, or at most just have set of extensions that you can use (kind of like it's done in AWS RDS or AWS Aurora). The claim is "serverless" i.e. you don't have access to the server and if you could install any extension you essentially have full access to the server as there's no restriction what you could do in an extension. I don't think that would be allowed.