metrics: adjust router and db buckets

Most HTTPS requests actually fall into the single-digit millisecond
range or below on average. Even the more costly endpoints almost always
average around the lower third of the millisecond magnitude.
Only endpoints doing synchronous remote HTTP fetches (e.g. for signing
keys) occasionally spike into the order of seconds.
As is, the bucket resolution is completely unfit to reason about
anything and even just averages are better indications.

Most database queries take less than a millisecond and even in total
almost all take less than 50ms for me. Decode time is but a tiny
fraction of that and queue time usually only takes a small part of total
time too (but may spike on high load).

Shift the buckets down to be able to
give insight into all relevant cases.
In particular this allows to determine whether high averages
are the result of generally high processing times or just a few
outliers lifting the whole average up (e.g. slow network fetches).

Exact numbers are biased towards my setup for lack of other comparison
data, but at least the order of magnitude should be ok everywhere.

lib/pleroma/web/telemetry.ex

@@ -130,7 +130,7 @@ defp distribution_metrics do
         unit: {:native, :second},
         tags: [:route],
         reporter_options: [
-          buckets: [0.1, 0.2, 0.5, 1, 2.5, 5, 10, 25, 50, 100, 250, 500, 1000]
+          buckets: [0.0005, 0.001, 0.005, 0.01, 0.025, 0.05, 0.10, 0.25, 0.5, 0.75, 1, 2, 5, 15]
         ]
       ),
 
@@ -232,8 +232,7 @@ defp summary_fallback_metrics(byte_unit \\ :byte) do
     # and we can use sum + counter to get the average between polls from their change
     # But for repo query times we need to use a full distribution
 
-    simple_buckets = [0, 1, 2, 4, 8, 16]
-    simple_buckets_quick = for t <- simple_buckets, do: t / 100.0
+    simple_buckets = [1, 2, 4, 8, 16, 32]
 
     # Already included in distribution metrics anyway:
     #   phoenix.router_dispatch.stop.duration
@@ -253,7 +252,7 @@ defp summary_fallback_metrics(byte_unit \\ :byte) do
         measurement: :decode_time,
         unit: {:native, :millisecond},
         reporter_options: [
-          buckets: simple_buckets_quick
+          buckets: [0.001, 0.0025, 0.005, 0.01, 0.02, 0.05, 0.1, 0.5]
         ]
       ),
       distribution("pleroma.repo.query.query_time.fdist",
@@ -261,7 +260,7 @@ defp summary_fallback_metrics(byte_unit \\ :byte) do
         measurement: :query_time,
         unit: {:native, :millisecond},
         reporter_options: [
-          buckets: simple_buckets
+          buckets: [0.1, 0.2, 0.5, 1, 1.5, 3, 5, 10, 25, 50]
         ]
       ),
       distribution("pleroma.repo.query.idle_time.fdist",