docs: Explanation - pin workloads to 0.130

docs/.custom_wordlist.txt

@@ -21,6 +21,7 @@ CMRs
 config
 configs
 contextualize
+contrib
 cpu
 cryptographic
 cryptographically

docs/reference/release-notes.md

@@ -27,8 +27,9 @@ COS 2 is compatible with Juju v3.6+. When deployed using terraform, Juju v3.6.11
   - [Telemetry correlation](../explanation/telemetry-correlation.md) is now automatically enabled when you deploy COS using the
     Terraform module.
 - **Grafana v12**. We upgraded the workload version from Grafana 9 to Grafana 12. A thorough review of Grafana's breaking changes and how they affect us is available [on Discourse](https://discourse.charmhub.io/t/cos-will-start-using-grafana-12-what-changed/18868).
-- **Opentelemetry collector**. Charmed opentelemetry-collector was released. The charm was designed to be a drop-in replacement for 
-  the grafana-agent charm (upstream grafana-agent is EOL since November 2025, and we will support charmed grafana-agent until July 2026).
+- **Opentelemetry collector**. Charmed opentelemetry-collector was released. The charm was designed to be a drop-in replacement for the grafana-agent charm (upstream grafana-agent is EOL since November 2025, and we will support charmed grafana-agent until July 2026).
+  - The workload is pinned to version 0.130 because the upstream `opentelemetry-collector-contrib` [project](https://github.com/open-telemetry/opentelemetry-collector-contrib) dropped support for Loki exporter in [release v0.131.0](https://github.com/open-telemetry/opentelemetry-collector-contrib/releases/tag/v0.131.0), stating that users can migrate to the OTLP exporters instead.
+    - The logging integrations for the `opentelemetry-collector` charms rely on `lokiexporter` to send logs to Loki push API endpoints. Loki only recently received upstream support for an OTLP endpoint, and migrating to an OTLP-first ecosystem in COS began in 26.04. The objective is to have support for OTLP ecosystem-wide by the end of 26.10 and to deprecate the Loki Push API feature (`logging` endpoint). Support will then be fully dropped in 27.04, and the `opentelemetry-collector` charms will no longer be pinned to `v0.130`.
 - `extra_alert_labels` config option. A new config option in grafana-agent and opentelemetry-collector enabled adding custom labels to alert rules. Custom labels are useful for differentiating alerts coming from sites with different SLAs.
 - **API links in catalogue-k8s**. The cards in catalogue-k8s now support extra links for documentation and APIs. COS charms now provide links to the workload API, making it easier to locate ingress URLs
 for workloads without a web UI.