add a flag to avoid non incremental size calculation in pageserver http api

This calculation is not that heavy but it is needed only in tests, and
in case the number of tenants/timelines is high the calculation can take
noticeable time.

Resolves https://github.com/zenithdb/zenith/issues/804

test_runner/fixtures/zenith_fixtures.py

@@ -610,7 +610,9 @@ class ZenithPageserverHttpClient(requests.Session):
         return res_json
 
     def branch_detail(self, tenant_id: uuid.UUID, name: str) -> Dict[Any, Any]:
-        res = self.get(f"http://localhost:{self.port}/v1/branch/{tenant_id.hex}/{name}", )
+        res = self.get(
+            f"http://localhost:{self.port}/v1/branch/{tenant_id.hex}/{name}?include-non-incremental-logical-size=1",
+        )
         res.raise_for_status()
         res_json = res.json()
         assert isinstance(res_json, dict)