Add sprint checklist to vacation checklist.

This PR adds the sprint checklist to the vacation checklist, to remind team members that they must complete the checklist before leaving.

JIRA tickets: https://tasks.opencraft.com/browse/SE-3841

Merge deadline: "None" if there's no rush, "ASAP" if it's critical, or provide a specific date if there is one.

Testing instructions:

1. Build the documentation per the README
2. Check over the text to verify the changes make sense and have been formatted correctly.

Reviewers

• @nizarmah