fix: email task listing for subsections

Improve task listing in reminder and notification emails.

Supporting information

• Jira ticket: https://tasks.opencraft.com/browse/BB-7556
• GitLab issue: #108 (closed)

Visual changes

Screenshots

Testing instructions

Step by step procedure

1. Get local stack running with dummy data using make oneshot command.
2. Create a recurrence and let it run once.
3. Open django shell using make shell and python manage.py shell.
4. Open logs in another shell using make logs
5. Run below snippet to see emails in logs

from django.core import mail
from workflow.tasks import *
from workflow.models import *
from datetime import timedelta
run = Run.objects.first()
with mail.get_connection() as conn:
    send_pending_checklist_email_for_runs(run, conn, timedelta(1))

6. Copy the email from logs and create a temporary html file to preview email in browser.