docs: Add release notes for 2.9.0 (#5298)

* docs: Add release notes for 2.9.0

Workflow run: https://github.com/HumanSignal/label-studio-enterprise/actions/runs/7545621956

* Moved date and added helm chart version

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Co-authored-by: robot-ci-heartex <robot-ci-heartex@users.noreply.github.com>
Co-authored-by: Caitlin Wheeless <caitlin.wheeless@gmail.com>

docs/source/guide/release_notes/onprem/2.9.0.md

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+---
+hide_sidebar: true
+---
+
+## Label Studio Enterprise 2.9.0
+
+*Jan 16, 2024*
+
+**[Helm chart](https://github.com/HumanSignal/charts/tree/master/heartex/label-studio) version:** 1.3.3
+
+### Enhancements
+
+- Improved webhook performance by assigning them to their own queue.
+
+- Adjusted spacing in the SCIM and SAML/SSO pages to improve readability.
+
+- When configuring SCIM with Okta, we will respond to their `userName` filter requests with the `email` attribute to ensure unique identifiers while maintaining compatibility.
+
+- When hovering over the **Submitted Annotations** card on the project dashboard, the tooltip will make it clear when the number includes skipped and empty annotations.
+
+
+### Security
+
+- Fixed an issue with HTML sanitization to address a vulnerability identified by CodeQL.
+
+
+### Bug fixes
+
+- Fixed some usability issues in the project Dashboards page related to the date picker and page refresh.
+
+- Fixed an issue where, when labeling tasks, hiding a region would create a draft and display the **Fix and Accept** action, even if no other changes had been made.
+
+- Fixed an issue where credential validation was failing in the Label Studio interface for cloud storages configured using SDK.
+