Hide empty sections

Summary:
Avoid dumping empty sections in config files.

I think they look weird in config
```toml
[tracing-headers]

[worker.snaphosts]
```

crates/types/src/config/common.rs

@@ -739,6 +739,8 @@ pub struct TracingOptions {
     ///
     /// Specify additional headers you want the system to send to the tracing endpoint (e.g.
     /// authentication headers).
+    #[serde(skip_serializing_if = "SerdeableHeaderHashMap::is_empty")]
+    #[serde(default)]
     pub tracing_headers: SerdeableHeaderHashMap,
 }
 

crates/types/src/config/worker.rs

@@ -68,6 +68,8 @@ pub struct WorkerOptions {
     ///
     /// Snapshots provide a mechanism for safely trimming the log and efficient bootstrapping of new
     /// worker nodes.
+    #[serde(skip_serializing_if = "is_default_snapshots_options")]
+    #[serde(default)]
     pub snapshots: SnapshotsOptions,
 }
 
@@ -366,7 +368,7 @@ impl Default for StorageOptions {
 ///
 /// Partition store snapshotting settings.
 #[serde_as]
-#[derive(Default, Debug, Clone, Serialize, Deserialize, derive_builder::Builder)]
+#[derive(Default, Debug, Clone, PartialEq, Eq, Serialize, Deserialize, derive_builder::Builder)]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 #[cfg_attr(feature = "schemars", schemars(rename = "SnapshotsOptions", default))]
 #[serde(rename_all = "kebab-case")]
@@ -402,6 +404,10 @@ pub struct SnapshotsOptions {
     pub snapshot_interval_num_records: Option<NonZeroU64>,
 }
 
+fn is_default_snapshots_options(opts: &SnapshotsOptions) -> bool {
+    opts == &SnapshotsOptions::default()
+}
+
 impl SnapshotsOptions {
     pub fn snapshots_base_dir(&self) -> PathBuf {
         super::data_dir("db-snapshots")