Fix updating "trace_read_requests" with /v1/tenant/config mgmt API.

The new "trace_read_requests" option was missing from the
parse_toml_tenant_conf function that reads the config file. Because of
that, the option was ignored, which caused the test_read_trace.py test
to fail. It used to work before commit 9a6c0be, because the
TenantConfigOpt struct was constructed directly in tenant_create_handler,
but now it is saved and read back from disk even for a newly created
tenant.

The abovementioned bug was fixed in commit 0939327 already, which
added the missing code to parse_toml_tenant_conf() to parse the
new "trace_read_requests" option. This commit fixes one more function
that was missed earlier, and adds more detail to the error message if
parsing the config file fails.

pageserver/src/tenant.rs

@@ -782,7 +782,7 @@ impl Tenant {
         let tenant_conf = match Self::load_tenant_config(conf, tenant_id) {
             Ok(conf) => conf,
             Err(e) => {
-                error!("load tenant config failed: {}", e);
+                error!("load tenant config failed: {:?}", e);
                 return Tenant::create_broken_tenant(conf, tenant_id);
             }
         };

pageserver/src/tenant_config.rs

@@ -185,6 +185,9 @@ impl TenantConfOpt {
         if let Some(max_lsn_wal_lag) = other.max_lsn_wal_lag {
             self.max_lsn_wal_lag = Some(max_lsn_wal_lag);
         }
+        if let Some(trace_read_requests) = other.trace_read_requests {
+            self.trace_read_requests = Some(trace_read_requests);
+        }
     }
 }