feat(storcon): timeline detach ancestor passthrough (#8353)

Currently storage controller does not support forwarding timeline detach
ancestor requests to pageservers. Add support for forwarding `PUT
.../:tenant_id/timelines/:timeline_id/detach_ancestor`. Implement the
support mostly as is, because the timeline detach ancestor will be made
(mostly) idempotent in future PR.

Cc: #6994

libs/pageserver_api/src/models/detach_ancestor.rs

@@ -1,6 +1,6 @@
 use utils::id::TimelineId;
 
-#[derive(Default, serde::Serialize)]
+#[derive(Debug, Default, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct AncestorDetached {
     pub reparented_timelines: Vec<TimelineId>,
 }