metrics: Don't unwrap client instantiation errors (#18018)

(cherry picked from commit 5cc0734)

Co-authored-by: Trent Nelson <trent@solana.com>

metrics/src/metrics.rs

@@ -103,16 +103,23 @@ impl MetricsWriter for InfluxDbMetricsWriter {
 
             let client = reqwest::blocking::Client::builder()
                 .timeout(Duration::from_secs(5))
-                .build()
-                .unwrap();
+                .build();
+            let client = match client {
+                Ok(client) => client,
+                Err(err) => {
+                    warn!("client instantiation failed: {}", err);
+                    return;
+                }
+            };
+
             let response = client.post(write_url.as_str()).body(line).send();
             if let Ok(resp) = response {
-                if !resp.status().is_success() {
-                    warn!(
-                        "submit response unsuccessful: {} {}",
-                        resp.status(),
-                        resp.text().unwrap()
-                    );
+                let status = resp.status();
+                if !status.is_success() {
+                    let text = resp
+                        .text()
+                        .unwrap_or_else(|_| "[text body empty]".to_string());
+                    warn!("submit response unsuccessful: {} {}", status, text,);
                 }
             } else {
                 warn!("submit error: {}", response.unwrap_err());