Add check_migrations command

this way, at least in the Docker setup, you'll get a meaningful error when you
try to start up a half-baked server

Dockerfile

@@ -32,4 +32,4 @@ RUN ["bugsink-manage", "migrate", "snappea", "--database=snappea"]
 
 EXPOSE 8000
 
-CMD [ "monofy", "bugsink-manage", "check", "--deploy", "--fail-level", "WARNING", "&&", "gunicorn", "--bind=0.0.0.0:8000", "--workers=10", "--access-logfile", "-", "bugsink.wsgi", "|||", "bugsink-runsnappea"]
+CMD [ "monofy", "bugsink-manage", "check_migrations", "&&", "bugsink-manage", "check", "--deploy", "--fail-level", "WARNING", "&&", "gunicorn", "--bind=0.0.0.0:8000", "--workers=10", "--access-logfile", "-", "bugsink.wsgi", "|||", "bugsink-runsnappea"]

ingest/management/commands/check_migrations.py

@@ -0,0 +1,24 @@
+from django.core.management import call_command
+from django.core.management.base import BaseCommand
+
+
+class Command(BaseCommand):
+    help = "Calls `migrate` with `check_unapplied=True` to check for unapplied migrations (2 DBs, adds error message)"
+
+    def handle(self, *args, **options):
+        try:
+            call_command('migrate', check_unapplied=True)
+        except SystemExit:
+            self.stdout.write(self.style.ERROR(
+                "You have unapplied migrations. Make sure to call `bugsink-manage migrate` before running the server."
+            ))
+            raise
+
+        try:
+            call_command('migrate', "snappea", check_unapplied=True, database="snappea")
+        except SystemExit:
+            self.stdout.write(self.style.ERROR(
+                "You have unapplied migrations. Make sure to call `bugsink-manage migrate snappea --database=snappea` "
+                "before running the server."
+            ))
+            raise