Simplify tls-rustls example (#254)

## Motivation

Current `tls-rustls` example might be inconvenient for some people.

## Solution

Rename current example to `low-level-rustls` and add a high level example in its place.

examples/low-level-rustls/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "example-low-level-rustls"
+version = "0.1.0"
+edition = "2018"
+publish = false
+
+[dependencies]
+axum = { path = "../.." }
+tokio = { version = "1.0", features = ["full"] }
+tracing = "0.1"
+tracing-subscriber = "0.2"
+tokio-rustls = "0.22.0"
+hyper = { version = "0.14", features = ["full"] }