Add missing regionendpoint documentation.

What does this MR do?

Add missing regionendpoint documentation.

Related issues

Closes #57718 (closed)

Author's checklist

• Apply the correct labels and milestone
• Crosslink the document from the higher-level index
• Crosslink the document from other subject-related docs
• Feature moving tiers? Make sure the change is also reflected in features.yml
• Correctly apply the product badges and tiers
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards

doc/administration/container_registry.md

@@ -388,7 +388,7 @@ So you must use an address that resolves and is accessible outside GitLab server
 **Omnibus GitLab installations**
 
 > **Note:**
-`regionendpoint` is optional. It's used as a endpoint for S3 compatible storage services (Minio, etc).
+`regionendpoint` is only required when configuring an S3 compatible service such as Minio, by entering a URL such as http://127.0.0.1:9000
 
 To configure the storage driver in Omnibus: