relay: Add the OOM invocation metrics

With this commit, a relay now emits metrics event on the MetricsPort
related to the OOM invocation for:

  - DNS cache
  - GeoIP database
  - Cell queues
  - HSDir caches

Everytime the OOM is invoked, the number of bytes is added to the
metrics counter for that specific type of invocation.

Related to #40367

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