chore(server): add comment server feature flags (#12993)

https://github.com/toeverything/AFFiNE/pull/12989#discussion_r2180167232



#### PR Dependency Tree


* **PR #12993** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

## Summary by CodeRabbit

* **New Features**
* The "Comment" feature is now recognized as a server feature and is
enabled by default.
* The server configuration and API schema have been updated to include
the "Comment" feature.

* **Tests**
* Added a new end-to-end test to verify that the "Comment" feature is
enabled by default.

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

packages/common/graphql/src/schema.ts

@@ -2345,6 +2345,7 @@ export enum ServerDeploymentType {
 
 export enum ServerFeature {
   Captcha = 'Captcha',
+  Comment = 'Comment',
   Copilot = 'Copilot',
   CopilotEmbedding = 'CopilotEmbedding',
   Indexer = 'Indexer',