docs: Release notes for Loki 3.4 (backport k239) (#16209)

Co-authored-by: J Stickler <[email protected]>

Author: loki-gh-app[bot]

docs/sources/release-notes/_index.md

@@ -8,6 +8,7 @@ weight: 100
 Release notes for Loki are in the CHANGELOG for the release and
 listed here by version number.
 
+- [V3.4 release notes](https://grafana.com/docs/loki/<LOKI_VERSION>/release-notes/v3-4/)
 - [V3.3 release notes](https://grafana.com/docs/loki/<LOKI_VERSION>/release-notes/v3-3/)
 - [V3.2 release notes](https://grafana.com/docs/loki/<LOKI_VERSION>/release-notes/v3-2/)
 - [V3.1 release notes](https://grafana.com/docs/loki/<LOKI_VERSION>/release-notes/v3-1/)