tests: prepare test_historic_storage_formats for --timelines-onto-safekeepers (#12214)

## Problem
`test_historic_storage_formats` uses `/tenant_import` to import historic
data. Tenant import does not create timelines onto safekeepers, because
they might already exist on some safekeeper set. If it does, then we may
end up with two different quorums accepting WAL for the same timeline.

If the tenant import is used in a real deployment, the administrator is
responsible for looking for the proper safekeeper set and migrate
timelines into storcon-managed timelines.

- Relates to https://github.com/neondatabase/neon/pull/11712

## Summary of changes
- Create timelines onto safekeepers manually after tenant import in
`test_historic_storage_formats`
- Add a note to tenant import that timelines will be not storcon-managed
after the import.

storage_controller/src/service.rs

@@ -6651,6 +6651,8 @@ impl Service {
 
     /// This is for debug/support only: assuming tenant data is already present in S3, we "create" a
     /// tenant with a very high generation number so that it will see the existing data.
+    /// It does not create timelines on safekeepers, because they might already exist on some
+    /// safekeeper set. So, the timelines are not storcon-managed after the import.
     pub(crate) async fn tenant_import(
         &self,
         tenant_id: TenantId,

test_runner/regress/test_compatibility.py

@@ -18,6 +18,7 @@ from fixtures.neon_fixtures import (
     NeonEnv,
     NeonEnvBuilder,
     PgBin,
+    Safekeeper,
     flush_ep_to_pageserver,
 )
 from fixtures.pageserver.http import PageserverApiException
@@ -26,6 +27,7 @@ from fixtures.pageserver.utils import (
 )
 from fixtures.pg_version import PgVersion
 from fixtures.remote_storage import RemoteStorageKind, S3Storage, s3_storage
+from fixtures.safekeeper.http import MembershipConfiguration
 from fixtures.workload import Workload
 
 if TYPE_CHECKING:
@@ -542,6 +544,24 @@ def test_historic_storage_formats(
     # All our artifacts should contain at least one timeline
     assert len(timelines) > 0
 
+    # Import tenant does not create the timeline on safekeepers,
+    # because it is a debug handler and the timeline may have already been
+    # created on some set of safekeepers.
+    # Create the timeline on safekeepers manually.
+    # TODO(diko): when we have the script/storcon handler to migrate
+    # the timeline to storcon, we can replace this code with it.
+    mconf = MembershipConfiguration(
+        generation=1,
+        members=Safekeeper.sks_to_safekeeper_ids([env.safekeepers[0]]),
+        new_members=None,
+    )
+    members_sks = Safekeeper.mconf_sks(env, mconf)
+
+    for timeline in timelines:
+        Safekeeper.create_timeline(
+            dataset.tenant_id, timeline["timeline_id"], env.pageserver, mconf, members_sks
+        )
+
     # TODO: ensure that the snapshots we're importing contain a sensible variety of content, at the very
     # least they should include a mixture of deltas and image layers.  Preferably they should also
     # contain some "exotic" stuff like aux files from logical replication.