Fix headline levels for metrics, trim trailing dot (#383)

Author: Simran-B

site/themes/arangodb-docs-theme/layouts/shortcodes/metrics.md

@@ -10,11 +10,11 @@
 {{- end }}
 {{- range $category, $metricGroup := $metricGroups.Get "metrics" }}{{/* Seems to get sorted implicitly */}}
 
-#### {{ $category }}
+### {{ $category }}
 
 {{ range $metric := $metricGroup }}
 
-##### {{ $metric.help }}
+#### {{ strings.TrimRight "." $metric.help }}
 
 {{ if eq $metric.type "histogram" -}}
 `{{ $metric.name }}` (basename)<br>