storcon: timetime table, creation and deletion (#11058)

This PR extends the storcon with basic safekeeper management of
timelines, mainly timeline creation and deletion. We want to make the
storcon manage safekeepers in the future. Timeline creation is
controlled by the `--timelines-onto-safekeepers` flag.

1. it adds the `timelines` and `safekeeper_timeline_pending_ops` tables
to the storcon db
2. extend code for the timeline creation and deletion
4. it adds per-safekeeper reconciler tasks 

TODO:

* maybe not immediately schedule reconciliations for deletions but have
a prior manual step
* tenant deletions
* add exclude API definitions (probably separate PR)
* how to choose safekeeper to do exclude on vs deletion? this can be a
bit hairy because the safekeeper might go offline in the meantime.
* error/failure case handling
* tests (cc test_explicit_timeline_creation from #11002)
* single safekeeper mode: we often only have one SK (in tests for
example)
* `notify-safekeepers` hook:
https://github.com/neondatabase/neon/issues/11163

TODOs implemented:

* cancellations of enqueued reconciliations on a per-timeline basis,
helpful if there is an ongoing deletion
* implement pending ops overwrite behavior
* load pending operations from db

RFC section for important reading:
[link](https://github.com/neondatabase/neon/blob/main/docs/rfcs/035-safekeeper-dynamic-membership-change.md#storage_controller-implementation)

Implements the bulk of #9011
Successor of #10440.

---------

Co-authored-by: Arseny Sher <sher-ars@yandex.ru>

libs/pageserver_api/src/models.rs

@@ -274,6 +274,31 @@ pub struct TimelineCreateRequest {
     pub mode: TimelineCreateRequestMode,
 }
 
+/// Storage controller specific extensions to [`TimelineInfo`].
+#[derive(Serialize, Deserialize, Clone)]
+pub struct TimelineCreateResponseStorcon {
+    #[serde(flatten)]
+    pub timeline_info: TimelineInfo,
+
+    pub safekeepers: Option<SafekeepersInfo>,
+}
+
+/// Safekeepers as returned in timeline creation request to storcon or pushed to
+/// cplane in the post migration hook.
+#[derive(Serialize, Deserialize, Clone)]
+pub struct SafekeepersInfo {
+    pub tenant_id: TenantId,
+    pub timeline_id: TimelineId,
+    pub generation: u32,
+    pub safekeepers: Vec<SafekeeperInfo>,
+}
+
+#[derive(Serialize, Deserialize, Clone)]
+pub struct SafekeeperInfo {
+    pub id: NodeId,
+    pub hostname: String,
+}
+
 #[derive(Serialize, Deserialize, Clone)]
 #[serde(untagged)]
 pub enum TimelineCreateRequestMode {