Added debug=2 in release profile to all examples.

This makes rtt output work right when using `cargo run` in release mode.

Debug was already enabled for release builds in some of the examples but
not all.

examples/stm32l5/Cargo.toml

@@ -27,3 +27,6 @@ heapless = { version = "0.7.5", default-features = false }
 rand_core = { version = "0.6.3", default-features = false }
 embedded-io = { version = "0.4.0", features = ["async"] }
 static_cell = { version = "1.1", features = ["nightly"]}
+
+[profile.release]
+debug = 2