This rustdoc is pretty good to explain the abstraction, but giving a concrete example such as Prometheus would make a complete understanding much easier. Even I still have a bit of trouble to figure it out as-is.
You don't have to specify Topology here. I think it's better to keep the trait bindings to the minimum. DiscordWebhookSender should be enough.
I think this trait is correct but the way it is implemented feels wrong. I understand that you currently only have the discord implementation and you interact directly with it. But I feel like there will be a use case where we will want to have simple getter and setters for common attributes of AlertChannelConfig. I don't see a 100% clear use case right now though.
A bit of rustdoc would be relevant here to explain the intended use of this trait.
I don't think webhook url deserves to be in this abstract trait. It is possible that the AlertChannel does not have a webhook, such as SMS, phone calls, SMTP.
I feel like this is not a correct abstraction. NotificationAdapter has a responsibility and Deployer has another. This is a strong smell of broken Single Responsibility principle, probably interface segregation too.
I think we can solve the dependency issue by introducing a T here :
Violates OCP : we want to allow external contributors to provide new backend implementations (that is, if we want to introduce the concept of monitoring backend right now or wait until the needs arises?)
