feat: add page on user metrics and add a plot

Author: sanjayankur31

source/General/Metrics.md

@@ -0,0 +1,13 @@
+(metrics)=
+# Usage metrics
+
+The plot shows the trend in number of OSBv2 users over time.
+It is periodically updated using the script [here](https://github.com/OpenSourceBrain/Documentation/blob/main/scripts/get-user-metrics.py).
+Please note that this script can only be run by OSBv2 administrators as it requires access to the user database that non-admin users will not have.
+
+```{figure} ../images/20250528-osb-users-plot.png
+:alt: Plot showing number of OSBv2 users over time
+:align: center
+:width: 600px
+
+```

source/_toc.yml

@@ -44,6 +44,7 @@ parts:
   - caption: Community
     chapters:
       - file: General/CoC
+      - file: General/Metrics
       - file: General/Contacts
       - file: General/Contribute_To_OSB
       - file: General/Contribute_To_OSB_docs