add information about alembic failures (#4262)

Signed-off-by: Benji Visser <benji@093b.org>

run_alembic_check.sh

@@ -3,4 +3,21 @@
 export PATH="${PATH}:.venv/bin"
 alembic upgrade head
 # then check if the database is up to date with the models
-alembic check
+if ! alembic check; then
+    echo ""
+    echo "============================================"
+    echo "ALEMBIC CHECK FAILED"
+    echo "============================================"
+    echo ""
+    echo "Your database models are out of sync with the migrations."
+    echo ""
+    echo "If this is an OSS sync PR and you had database migrations"
+    echo "in your cloud PR, you will need to generate the migration"
+    echo "for this branch:"
+    echo ""
+    echo "  alembic revision --autogenerate -m \"your migration description\""
+    echo ""
+    echo "Then commit and push the generated migration file to this branch."
+    echo ""
+    exit 1
+fi