[AI] [Inference] update changelog to pass release process (#30240)

### Packages impacted by this PR
@azure-rest/ai-inference

### Issues associated with this PR


### Describe the problem that is addressed by this PR
Add date and required subheader to changelog

### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?


### Are there test cases added in this PR? _(If not, why?)_


### Provide a list of related PRs _(if any)_


### Command used to generate this PR:**_(Applicable only to SDK release
request PRs)_

### Checklists
- [ ] Added impacted package name to the issue description
- [ ] Does this PR needs any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
repository and link it here)_
- [ ] Added a changelog (if necessary)

sdk/ai/ai-inference-rest/CHANGELOG.md

@@ -1,5 +1,6 @@
 # Release History
 
-## 1.0.0-beta.1 (Unreleased)
+## 1.0.0-beta.1 (2024-06-30)
 
+### Features Added
 - This is the initial beta release for the Azure AI Inference SDK, which is a common API supporting Azure AI Inference models.