changes: File for ticket 40063, the MetricsPort

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

changes/ticket40063

+  o Major features (metrics):
+    - Introduce a new MetricsPort which exposes, through an HTTP GET /metrics, a
+      series of metrics that tor collects at runtime. At the moment, the only
+      supported output format is Prometheus data model. Closes ticket 40063;
+