add freshness policy assets and repository to toys (#29295)

## Summary & Motivation
Add a dedicated repository and a few assets with internal freshness policies to toys

## How I Tested These Changes

## Changelog

> Insert changelog entry or delete this section.

Author: anuthebananu

Diff for: python_modules/dagster-test/dagster_test/toys/freshness.py

@@ -0,0 +1,35 @@
+from datetime import timedelta
+
+import dagster as dg
+from dagster._core.definitions.freshness import InternalFreshnessPolicy
+
+
+@dg.asset(
+    internal_freshness_policy=InternalFreshnessPolicy.time_window(fail_window=timedelta(minutes=60))
+)
+def asset_with_time_window_freshness_60m():
+    return 1
+
+
+@dg.asset(
+    internal_freshness_policy=InternalFreshnessPolicy.time_window(fail_window=timedelta(minutes=30))
+)
+def asset_with_time_window_freshness_30m():
+    return 1
+
+
+@dg.asset(
+    internal_freshness_policy=InternalFreshnessPolicy.time_window(
+        fail_window=timedelta(minutes=15), warn_window=timedelta(minutes=10)
+    )
+)
+def asset_with_time_window_freshness_and_warning():
+    return 1
+
+
+def get_freshness_assets():
+    return [
+        asset_with_time_window_freshness_60m,
+        asset_with_time_window_freshness_30m,
+        asset_with_time_window_freshness_and_warning,
+    ]

Diff for: python_modules/dagster-test/dagster_test/toys/repo.py

@@ -234,3 +234,10 @@ def asset_health_repository():
     from dagster_test.toys.asset_health import get_assets_and_checks
 
     return get_assets_and_checks()
+
+
+@repository
+def freshness_repository():
+    from dagster_test.toys.freshness import get_freshness_assets
+
+    return get_freshness_assets()