Feature: compute timings on the day plan table of contents

**Which module(s) and week(s) does this change affect?**
all day plans
**What is the work that needs to be done?**

Given a day plan https://programming.codeyourfuture.io/user-data/sprints/1/day-plan/
When I look at the table of contents in the page header https://programming.codeyourfuture.io/user-data/sprints/1/day-plan/#toc
Then each heading has a start and end time

**Why is this work important to do?**

An overview agenda as well as a detailed one is emerging as a user need

**Additional context**

The times are computed by a web component called time-stamper on the main run of the day plan. I don't think the component is really reusable in this case but maybe I'm wrong!

Here's the day plan docs

https://common.codeyourfuture.io/common-theme/pages/day-plan/

here's the page header that generates the table of contents
https://github.com/CodeYourFuture/curriculum/blob/874907ac6f636e00e745ae1b79c6c429957e0eef/common-theme/layouts/partials/page-header.html

You only want this feature on the day plan, so likely you will have to branch into a new partial to generate this

**Who might need to know about this change?**