feat(alerts): use the meta description in source freshness alerts

docs/_snippets/guides/alerts-code-configuration.mdx

@@ -141,7 +141,7 @@ tests:
 
 #### Test description
 
-Elementary supports configuring description for tests that are included in alerts.
+Elementary supports configuring description for tests and source freshness checks that are included in alerts.
 It's recommended to add an explanation of what does it mean if this test fails, so alert will include this context.
 
 <CodeGroup>
@@ -170,6 +170,15 @@ tests:
         description: "This is the test description"
 ```
 
+```yml source
+sources:
+  - name: my_source
+    tables:
+      - name: my_table
+        meta:
+          description: "This is the source freshness description"
+```
+
 </CodeGroup>
 
 #### Tags

elementary/monitor/fetchers/alerts/schema/alert_data.py

@@ -350,7 +350,7 @@ def format_alert(
             max_loaded_at=self.max_loaded_at,
             max_loaded_at_time_ago_in_s=self.max_loaded_at_time_ago_in_s,
             filter=self.filter,
-            freshness_description=self.freshness_description,
+            freshness_description=self.description or self.freshness_description,
             alert_class_id=self.alert_class_id,
             model_unique_id=self.model_unique_id,
             detected_at=self.detected_at,

tests/unit/monitor/fetchers/alerts/schemas/test_alert_data_schema.py

@@ -5,6 +5,7 @@
 
 from elementary.monitor.fetchers.alerts.schema.alert_data import (
     BaseAlertDataSchema,
+    SourceFreshnessAlertDataSchema,
     TestAlertDataSchema,
 )
 from elementary.utils.time import DATETIME_FORMAT
@@ -37,6 +38,15 @@
     test_meta=dict(),
     elementary_unique_id="e_id_1"
 )
+SOURCE_FRESHNESS_ALERT = dict(
+    **BASE_ALERT,
+    source_freshness_execution_id="sfe_id_1",
+    source_name="source_1",
+    identifier="table_1",
+    original_status="error",
+    path="models/sources.yml",
+    freshness_description="default"
+)
 
 
 def test_flatten_meta():
@@ -119,3 +129,18 @@ def test_tags():
 
     base_alert = BaseAlertDataSchema(**{**BASE_ALERT, "tags": "a"})
     assert sorted(base_alert.tags) == sorted(["a"])
+
+
+@pytest.mark.parametrize(
+    "model_meta,expected",
+    [
+        (dict(), "default"),
+        (dict(description="custom"), "custom"),
+        (dict(alerts_config=dict(description="custom")), "custom"),
+    ],
+)
+def test_source_freshness_alert_description(model_meta, expected):
+    alert_data = SourceFreshnessAlertDataSchema(
+        **{**SOURCE_FRESHNESS_ALERT, "model_meta": model_meta}
+    )
+    assert alert_data.format_alert().freshness_description == expected