Healthz endpoints for Driver and Solvers (#2060)

# Description
Adds liveness endpoints for `driver` and `solvers` crates.

# Changes
2 new GET endpoints always returning `200OK`

## How to test
Will be tested in scope of the
cowprotocol/infrastructure#858 deployment

## Related Issues

Fixes #1382

crates/driver/src/infra/api/mod.rs

@@ -43,8 +43,9 @@ impl Api {
         let tokens = tokens::Fetcher::new(self.eth.clone());
         let pre_processor = domain::competition::AuctionProcessor::new(Arc::new(self.eth.clone()));
 
-        // Add the metrics endpoint.
+        // Add the metrics and healthz endpoints.
         app = routes::metrics(app);
+        app = routes::healthz(app);
 
         // Multiplex each solver as part of the API. Multiple solvers are multiplexed
         // on the same driver so only one liquidity collector collects the liquidity

crates/driver/src/infra/api/routes/healthz.rs

@@ -0,0 +1,9 @@
+use axum::{http::StatusCode, response::IntoResponse, routing::get};
+
+pub(in crate::infra::api) fn healthz(app: axum::Router<()>) -> axum::Router<()> {
+    app.route("/healthz", get(route))
+}
+
+async fn route() -> impl IntoResponse {
+    StatusCode::OK
+}

crates/driver/src/infra/api/routes/mod.rs

@@ -1,3 +1,4 @@
+mod healthz;
 mod info;
 mod metrics;
 mod quote;
@@ -6,6 +7,7 @@ mod settle;
 mod solve;
 
 pub(super) use {
+    healthz::healthz,
     info::info,
     metrics::metrics,
     quote::{quote, OrderError},

crates/solvers/src/api/mod.rs

@@ -20,6 +20,7 @@ impl Api {
         shutdown: impl Future<Output = ()> + Send + 'static,
     ) -> Result<(), hyper::Error> {
         let app = axum::Router::new()
+            .route("/healthz", axum::routing::get(routes::healthz))
             .route("/solve", axum::routing::post(routes::solve))
             .route("/notify", axum::routing::post(routes::notify))
             .layer(

crates/solvers/src/api/routes/healthz.rs

@@ -0,0 +1,5 @@
+use axum::{http::StatusCode, response::IntoResponse};
+
+pub async fn healthz() -> impl IntoResponse {
+    StatusCode::OK
+}

crates/solvers/src/api/routes/mod.rs

@@ -1,9 +1,10 @@
 use serde::Serialize;
 
+mod healthz;
 mod notify;
 mod solve;
 
-pub(super) use {notify::notify, solve::solve};
+pub(super) use {healthz::healthz, notify::notify, solve::solve};
 
 #[derive(Debug, Serialize)]
 #[serde(untagged)]