[DOCS] Kibana release notes for 9.1.8 (#244273)

Fixes elastic/docs-content#4093

Preview:
https://docs-v3-preview.elastic.dev/elastic/kibana/pull/244273/release-notes#kibana-9.1.8-release-notes

---------

Co-authored-by: wajihaparvez <[email protected]>

Author: nastasha-solomon

docs/release-notes/index.md

@@ -266,6 +266,53 @@ For the Elastic Security 9.2.0 release information, refer to [Elastic Security S
 * Fixes an accessibility issue where resetting changes or removing all terms in the Synonyms panel was not announced by screen readers. VoiceOver users on Safari will now hear updates when terms are reset [#237877]({{kib-pull}}237877).
 * Fixes an issue with a null property being read in Playground [#230729]({{kib-pull}}230729).
 
+## 9.1.8 [kibana-9.1.8-release-notes]
+
+% ::::{NOTE}
+% ::::
+
+
+### Features and enhancements [kibana-9.1.8-features-enhancements]
+
+**Elastic Observability solution**:
+For the Elastic Observability 9.1.8 release information, refer to [Elastic Observability Solution Release Notes](docs-content://release-notes/elastic-observability/index.md).
+
+**Elastic Security solution**:
+For the Elastic Security 9.1.8 release information, refer to [Elastic Security Solution Release Notes](docs-content://release-notes/elastic-security/index.md).
+
+
+### Fixes [kibana-9.1.8-fixes]
+
+**Alerting and cases**:
+* Captures connector errors without interrupting the case creation flow. Issues with connectors can be resolved on the case details page  [#244188]({{kib-pull}}244188).
+* Fixes pagination for the **Alerts** table, which was getting stuck on rule details pages [#242275]({{kib-pull}}242275).
+* Fetches tracked alerts without depending on the task state [#235253]({{kib-pull}}235253).
+
+**Dashboards and Visualizations**:
+* Fixes error that occurs when you deselect the **(blank)** option from the filter controls menu [#242036]({{kib-pull}}242036).
+
+**Data ingestion and Fleet**:
+* Uses long expiration for upgrading agents [#243443]({{kib-pull}}243443).
+* Fixes retrying agents stuck in auto-upgrade logic [#243326]({{kib-pull}}243326).
+* Adds retry behavior for `/api/fleet/agents` when transient issues with {{es}} are encountered [#243105]({{kib-pull}}243105).
+* Fixes Docker image in the **Add agent** Kubernetes manifest [#242691]({{kib-pull}}242691).
+* Fixes {{fleet}} policy name uniqueness not being consistently enforced across spaces when name or space changes occur [#239631]({{kib-pull}}239631).
+* Fixes `ignore_above` mapping for `flattened` fields [#238890]({{kib-pull}}238890).
+
+**Elastic Observability solution**:
+For the Elastic Observability 9.1.8 release information, refer to [Elastic Observability Solution Release Notes](docs-content://release-notes/elastic-observability/index.md).
+
+**Elastic Security solution**:
+For the Elastic Security 9.1.8 release information, refer to [Elastic Security Solution Release Notes](docs-content://release-notes/elastic-security/index.md).
+
+**Kibana platform**:
+* Fixes the production build favicon's CSS specificity [#243351]({{kib-pull}}243351).
+* Fixes an issue on the **Index management** page where screen reader text was different from visible text [#243802]({{kib-pull}}243802).
+* Fixes an issue with keyboard focus getting trapped on pages using document preview [#243791]({{kib-pull}}243791).
+
+**Machine Learning**:
+* Ensures deleted text in AI connector or Inference endpoint forms is not sent as empty strings [#244059]({{kib-pull}}244059).
+* Fixes import and improves validation for Anomaly Detection and Data Frame Analytics jobs [#242263]({{kib-pull}}242263).
 
 ## 9.1.7 [kibana-9.1.7-release-notes]