Classes functions (etc) should have a header in the documentation

[Sarah Boyce]

Currently, the docs are slightly inconsistent whether classes/functions have their own header or not.
For example:

• ​https://docs.djangoproject.com/en/5.2/ref/utils/ lacks headers for many functions e.g. ​https://docs.djangoproject.com/en/5.2/ref/utils/#django.utils.cache.patch_cache_control
• ​https://docs.djangoproject.com/en/5.2/ref/models/fields/ has generous headers

Following a conversation on the forum, being generous with headers is preferable because:

• it improves the table of contents to make it easier to navigate the page for all users
• the page is more accessible to screen reader users as they can navigate via headers
• (minor) the djangoproject.com docs search checks the table of contents when ranking search results (so adding headers improves the search results)

The discussion is here: ​https://forum.djangoproject.com/t/set-toc-object-entries-true-to-auto-add-functions-classes-to-the-pages-table-of-contents/38902/7

I propose that we add that we should have a "duplicate" header above the class/function definition to our writing documentation guide: ​https://docs.djangoproject.com/en/5.2/internals/contributing/writing-documentation/#guidelines-for-restructuredtext-files