Fix synthetics docs for read-only user !! (#2632)

This seems a bug which we should fixed, for synthetics read only user we
only need read permissions !!

Flagged by a user elastic/enhancements#25472

Author: shahzad31

solutions/observability/synthetics/reader-role.md

@@ -28,5 +28,5 @@ Instead to you can create a reader role, called something like `synthetics_reade
 | --- | --- | --- |
 | [Index](/deploy-manage/users-roles/cluster-or-deployment-auth/elasticsearch-privileges.md#privileges-list-indices) | `synthetics-*`: `read` | Read-only access to synthetics indices. |
 | [Index](/deploy-manage/users-roles/cluster-or-deployment-auth/elasticsearch-privileges.md#privileges-list-indices) | `.alerts-observability.uptime.alerts-*`: `read` | Read-only access to synthetics alert indices. |
-| [Kibana](/deploy-manage/users-roles/cluster-or-deployment-auth/kibana-privileges.md) | `Synthetics and Uptime`: `All` | Access to the {{synthetics-app}} in {{kib}}. |
+| [Kibana](/deploy-manage/users-roles/cluster-or-deployment-auth/kibana-privileges.md) | `Synthetics and Uptime`: `read` | Access to the {{synthetics-app}} in {{kib}}. |