Update dependencies and add admin module with metrics

- Global dependencies updated in Cargo.lock
- New module created in src/admin to host:
  - the (future) admin REST API
  - the metric collection
- add configuration block

No metrics implemented yet

src/util/config.rs

@@ -73,6 +73,9 @@ pub struct Config {
 
 	/// Configuration for serving files as normal web server
 	pub s3_web: WebConfig,
+
+	/// Configuration for the admin API endpoint
+	pub admin_api: AdminConfig,
 }
 
 /// Configuration for S3 api
@@ -96,6 +99,13 @@ pub struct WebConfig {
 	pub root_domain: String,
 }
 
+/// Configuration for the admin and monitoring HTTP API
+#[derive(Deserialize, Debug, Clone)]
+pub struct AdminConfig {
+	/// Address and port to bind for admin API serving
+	pub bind_addr: SocketAddr,
+}
+
 fn default_sled_cache_capacity() -> u64 {
 	128 * 1024 * 1024
 }