fix: Only trigger restart if current user is an instance admin. (#37227)

## Description
> [!TIP]  
> _Add a TL;DR when the description is longer than 500 words or
extremely technical (helps the content, marketing, and DevRel team)._
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> _Please also include relevant motivation and context. List any
dependencies that are required for this change. Add links to Notion,
Figma or any other documents that might be relevant to the PR._


Fixes #`Issue Number`  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._

## Automation

/ok-to-test tags="@tag.Sanity"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/11681598792>
> Commit: 4fa5ebc
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=11681598792&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Sanity`
> Spec:
> <hr>Tue, 05 Nov 2024 10:24:09 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
	- Enhanced user context processing during the restart operation.
	- Improved error handling and configuration for sending test emails.

- **Bug Fixes**
- Addressed issues related to connection testing and email sending with
detailed error messages.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/server/appsmith-server/src/main/java/com/appsmith/server/solutions/ce/EnvManagerCEImpl.java

@@ -725,7 +725,7 @@ public Mono<User> verifyCurrentUserIsSuper() {
 
     @Override
     public Mono<Void> restart() {
-        return verifyCurrentUserIsSuper().then(restartWithoutAclCheck());
+        return verifyCurrentUserIsSuper().flatMap(user -> restartWithoutAclCheck());
     }
 
     /**