feat(storage-controller): add node shards api (#8896)

For control-plane managed tenants, we have the page in the admin console
that lists all tenants on a specific pageserver. But for
storage-controller managed ones, we don't have that functionality for
now.

## Summary of changes

Adds an API that lists all shards on a given node (intention + observed)

---------

Signed-off-by: Alex Chi Z <chi@neon.tech>

libs/pageserver_api/src/controller_api.rs

@@ -112,6 +112,21 @@ pub struct TenantDescribeResponse {
     pub config: TenantConfig,
 }
 
+#[derive(Serialize, Deserialize, Debug)]
+pub struct NodeShardResponse {
+    pub node_id: NodeId,
+    pub shards: Vec<NodeShard>,
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+pub struct NodeShard {
+    pub tenant_shard_id: TenantShardId,
+    /// Whether the shard is observed secondary on a specific node. True = yes, False = no, None = not on this node.
+    pub is_observed_secondary: Option<bool>,
+    /// Whether the shard is intended to be a secondary on a specific node. True = yes, False = no, None = not on this node.
+    pub is_intended_secondary: Option<bool>,
+}
+
 #[derive(Serialize, Deserialize)]
 pub struct NodeDescribeResponse {
     pub id: NodeId,