metrics: Add HS service side circuit build time metrics.

This adds 2 histogram metrics for hidden services:
* `tor_hs_rend_circ_build_time` - the rendezvous circuit build time in milliseconds
* `tor_hs_intro_circ_build_time` - the introduction circuit build time in milliseconds

The text representation representation of the new metrics looks like this:
```
# HELP tor_hs_rend_circ_build_time The rendezvous circuit build time in milliseconds
# TYPE tor_hs_rend_circ_build_time histogram
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="1000.00"} 2
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="5000.00"} 10
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="10000.00"} 10
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="30000.00"} 10
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="60000.00"} 10
tor_hs_rend_circ_build_time_bucket{onion="<elided>",le="+Inf"} 10
tor_hs_rend_circ_build_time_sum{onion="<elided>"} 10824
tor_hs_rend_circ_build_time_count{onion="<elided>"} 10
# HELP tor_hs_intro_circ_build_time The introduction circuit build time in milliseconds
# TYPE tor_hs_intro_circ_build_time histogram
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="1000.00"} 0
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="5000.00"} 6
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="10000.00"} 6
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="30000.00"} 6
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="60000.00"} 6
tor_hs_intro_circ_build_time_bucket{onion="<elided>",le="+Inf"} 6
tor_hs_intro_circ_build_time_sum{onion="<elided>"} 9843
tor_hs_intro_circ_build_time_count{onion="<elided>"} 6
```

Signed-off-by: Gabriela Moldovan <gabi@torproject.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/feature/hs/hs_metrics_entry.h b/src/feature/hs/hs_metrics_entry.h
index b966f0c226..4c9abd06d7 100644
--- a/src/feature/hs/hs_metrics_entry.h
+++ b/src/feature/hs/hs_metrics_entry.h
@@ -58,6 +58,10 @@ typedef enum {
   HS_METRICS_NUM_ESTABLISHED_INTRO = 6,
   /** Number of rejected introducton requests. */
   HS_METRICS_NUM_REJECTED_INTRO_REQ = 7,
+  /** Introduction circuit build time in milliseconds. */
+  HS_METRICS_INTRO_CIRC_BUILD_TIME = 8,
+  /** Rendezvous circuit build time in milliseconds. */
+  HS_METRICS_REND_CIRC_BUILD_TIME = 9,
 } hs_metrics_key_t;
 
 /** The metadata of an HS metrics. */