feat: add NC_DISABLE_SUPPORT_CHAT environment variable documentation

Author: DarkPhoenix2704

content/self-hosting/environment-variables.mdx

@@ -135,6 +135,7 @@ has the required permissions. To disable it, set the `NC_DISABLE_PG_DATA_REFLECT
 
 | Variable          | Mandatory | Description                                                                                                                                                                                  | If Not Set |
 |-------------------|-----------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------|
+| `NC_DISABLE_SUPPORT_CHAT` | No | Disables the support chat within the product. We use Chatwoot which is an open source support system. | FALSE |
 | `NC_DISABLE_TELE` | No        | Disables the telemetry to prevent sending anonymous usage data. Please keep it enabled to help us understand the usage of the product and the impact that any new breaking change can cause. |            |
 
 ## Litestream