main: Specialize the periodic events on a per-role basis

In tor, we have a series of possible "roles" that the tor daemon can be
enabled for. They are:

  Client, Bridge, Relay, Authority (directory or bridge) and Onion service.

They can be combined sometimes. For instance, a Directory Authority is also a
Relay. This adds a "roles" field to a periodic event item object which is used
to know for which roles the event is for.

The next step is to enable the event only if the roles apply. No behavior
change at this commit.

Pars of #25762

Signed-off-by: David Goulet <dgoulet@torproject.org>