submission_date set on application submit; refactored index.py; display of expired in both home page and domain detail page

src/registrar/models/domain_application.py

@@ -6,6 +6,7 @@ import logging
 from django.apps import apps
 from django.db import models
 from django_fsm import FSMField, transition  # type: ignore
+from django.utils import timezone
 from registrar.models.domain import Domain
 
 from .utility.time_stamped_model import TimeStampedModel
@@ -615,6 +616,10 @@ class DomainApplication(TimeStampedModel):
         if not DraftDomain.string_could_be_domain(self.requested_domain.name):
             raise ValueError("Requested domain is not a valid domain name.")
 
+        # Update submission_date to today
+        self.submission_date = timezone.now().date()
+        self.save()
+
         self._send_status_update_email(
             "submission confirmation",
             "emails/submission_confirmation.txt",