feat(pageserver): add force patch index_part API (#11119)

## Problem

As part of the disaster recovery tool. Partly for
https://github.com/neondatabase/neon/issues/9114.

## Summary of changes

* Add a new pageserver API to force patch the fields in index_part and
modify the timeline internal structures.

---------

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

test_runner/fixtures/pageserver/http.py

@@ -375,6 +375,19 @@ class PageserverHttpClient(requests.Session, MetricsGetter):
         res = self.post(f"http://localhost:{self.port}/v1/tenant/{tenant_id}/reset", params=params)
         self.verbose_error(res)
 
+    def timeline_patch_index_part(
+        self,
+        tenant_id: TenantId | TenantShardId,
+        timeline_id: TimelineId,
+        data: dict[str, Any],
+    ):
+        res = self.post(
+            f"http://localhost:{self.port}/v1/tenant/{tenant_id}/timeline/{timeline_id}/patch_index_part",
+            json=data,
+        )
+        self.verbose_error(res)
+        return res.json()
+
     def tenant_location_conf(
         self,
         tenant_id: TenantId | TenantShardId,