docs: Add section why region.name is ignored

Author: Techassi

docs/modules/druid/partials/s3-note.adoc

@@ -3,5 +3,8 @@
 You can specify just a connection/bucket for either ingestion or deep storage or for both, but Druid only supports a single S3 connection under the hood.
 If two connections are specified, they must be the same. This is easiest if a dedicated S3 Connection Resource is used - not defined inline but as a dedicated object.
 
+The connection/bucket `region.name` field is ignored because Druid uses the AWS SDK v1, which ignores the region if the endpoint is set.
+The host is a required field, therefore the endpoint will always be set.
+
 TLS for S3 is not yet supported.
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