Update CHANGELOG with initial preview features

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: saleelpk

sdk/monitor/azure-mgmt-monitorslis/CHANGELOG.md

@@ -2,6 +2,17 @@
 
 ## 1.0.0b1 (2026-04-22)
 
+### Features Added
+
+- Initial preview release of `azure-mgmt-monitorslis` for managing
+  Service Level Indicator (SLI) resources under the `Microsoft.Monitor` namespace.
+- Support for SLI resource CRUD operations: create or update, get, delete, and list.
+- SLI evaluation with Availability and Latency categories, supporting both
+  window-based and request-based evaluation types with configurable signal sources,
+  aggregation, and SLO baselines.
+- Integration with Azure Monitor Workspace (AMW) accounts for metric emission,
+  with managed identity and alert support.
+
 ### Other Changes
 
   - Initial version