Clarify S3 region is required

When the Workhorse S3 client is used, the AWS SDK will raise an error if
`region` isn't specified. Clarify in the documentation that this must be
specified.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/297227

doc/administration/object_storage.md

@@ -232,7 +232,7 @@ The connection settings match those provided by [fog-aws](https://github.com/fog
 | `aws_secret_access_key` | AWS credentials, or compatible | |
 | `aws_signature_version` | AWS signature version to use. `2` or `4` are valid options. Digital Ocean Spaces and other providers may need `2`. | `4` |
 | `enable_signature_v4_streaming` | Set to `true` to enable HTTP chunked transfers with [AWS v4 signatures](https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-streaming.html). Oracle Cloud S3 needs this to be `false`. | `true` |
-| `region` | AWS region | us-east-1 |
+| `region` | AWS region. | |
 | `host` | S3 compatible host for when not using AWS, e.g. `localhost` or `storage.example.com`. HTTPS and port 443 is assumed. | `s3.amazonaws.com` |
 | `endpoint` | Can be used when configuring an S3 compatible service such as [MinIO](https://min.io), by entering a URL such as `http://127.0.0.1:9000`. This takes precedence over `host`. | (optional) |
 | `path_style` | Set to `true` to use `host/bucket_name/object` style paths instead of `bucket_name.host/object`. Leave as `false` for AWS S3. | `false` |