Document how to manually close database connections

[Baptiste Mispelon]

I was reading about manual database connection management today and came upon this section (emphasis mine) [1]:

If a connection is created in a long-running process, outside of Django’s request-response cycle, the connection will remain open until explicitly closed, or timeout occurs.

From what I understand, manually closing open db connections is done by calling django.db.close_old_connections(), but that function does not seem to be documented officially.
I'm not sure if the function is undocumented by design (it is after all a pretty unusual use-case and most users should never have to call it themselves), or if that was just an omission.

[1] ​https://docs.djangoproject.com/en/dev/ref/databases/#caveats

[Mariusz Felisiak]

I think it's fine to at least mention it in the "Caveats" section.

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In 184d82d:

Fixed #35130 -- Doc'd django.db.close_old_connections().

This also adds close_db_connections() to the django.db.all.