Like we did before for the resolver, a dialer should propagate the
request to close idle connections to underlying types.
See https://github.com/ooni/probe/issues/1591
Auto-configure every relevant TLS field as close as possible to
where it's actually used.
As a side effect, add support for mocking the creation of a TLS
connection, which should possibly be useful for uTLS?
Work that is part of https://github.com/ooni/probe/issues/1505
