[core] CHANGELOG date for @azure-rest/core-client release (#29440)

### Packages impacted by this PR

- `@azure-rest/core-client`

### Describe the problem that is addressed by this PR

Update CHANGELOG with release date to unblock release.

Author: timovv

sdk/core/core-client-rest/CHANGELOG.md

@@ -1,17 +1,11 @@
 # Release History
 
-## 2.0.0 (Unreleased)
-
-### Features Added
+## 2.0.0 (2024-04-25)
 
 ### Breaking Changes
 
 - Changed the format accepted for `multipart/form-data` requests.
 
-### Bugs Fixed
-
-### Other Changes
-
 ## 1.4.0 (2024-04-09)
 
 ### Features Added