Improve documentation for the fullstack crate (#2952)

* improve documentation for the fullstack server context

* Add a section about axum integration to the crate root docs

* make serve_dioxus_application accept the cfg builder directly

* remove unused server_fn module

* improve fullstack config docs

* improve documentation for the server function macro

* fix axum router extension link

* Fix doc tests

* Fix launch builder

* Remove redundant server_only inside server function

* Fix isrg config path

examples/fullstack-streaming/Cargo.toml

@@ -20,5 +20,5 @@ once_cell = "1.19.0"
 
 [features]
 default = []
-server = ["dioxus/axum", "tokio"]
+server = ["dioxus/axum", "dep:tokio"]
 web = ["dioxus/web"]