tor_bug_reached_count: distinct labels for non-fatal asserts

This is a variation of #40930 but it could also be combined with it.

Problem

The current rate of tor_bug_reached_count is so high on our exit relays (>> 1 per second) that we would need some way to tell relevant from not so relevant events.

Idea

Have distinct labels for non-fatal asserts vs. the one that got added in #40924 (closed)

This could look like this:

tor_bug_reached_count{bugtype=non_fatal_assert} 3
tor_bug_reached_count{bugtype=ld_bug} 20978