docs: add new otel links and grafana (#1788)

* docs: add new otel links and grafana

* docs: add new links

* Apply suggestions from code review

Author: jcstein

how-to-guides/celestia-node-metrics.md

@@ -48,10 +48,20 @@ Here is an example for Mocha testnet:
 
 ```sh
 celestia <node-type> start --metrics.tls=true \
-    --metrics --metrics.endpoint otel.celestia-mocha.com \
+    --metrics --metrics.endpoint otel.mocha.celestia.observer \
     --core.ip <URI> --p2p.network mocha
 ```
 
+### Arabica devnet
+
+Here is an example for Arabica devnet:
+
+```sh
+celestia <node-type> start --metrics.tls=true \
+    --metrics --metrics.endpoint otel.arabica.celestia.observer \
+    --core.ip <URI> --p2p.network arabica
+```
+
 ### TLS connections
 
 The `--metrics.tls` flag enables or disables a TLS connection to the

how-to-guides/mainnet.md

@@ -254,7 +254,7 @@ RPCs for DA nodes to initialise or start your celestia-node to Mainnet Beta with
 
 DA full and light nodes might have troubles connecting to the networks, so you
 can check out this
-[Grafana dashboard](https://celestia.grafana.net/public-dashboards/a10eff0043bb4bf0839004e2746e2bc6)
+[Grafana dashboard](https://celestia.observer/grafana)
 to see health/uptime status of DA bootstrappers (now `celestia` network only).
 
 You can [find the status of these endpoints](https://celestia-tools.brightlystake.com/).