chore(releasing): Add upgrade note for 0.31.0 about S3 path changes (#17934)

Closes: #17927

Signed-off-by: Jesse Szwedko <[email protected]>

---------

Signed-off-by: Jesse Szwedko <[email protected]>

Author: jszwedko

.github/actions/spelling/allow.txt

@@ -36,6 +36,7 @@ Celkon
 Ceph
 Chromecast
 Citrix
+Cloudflare
 Cloudfone
 Cmx
 Coby

website/content/en/highlights/2023-07-05-0-31-0-upgrade-guide.md

@@ -14,6 +14,10 @@ Vector's 0.31.0 release includes **breaking changes**:
 1. [Removal of various deprecated internal metrics](#deprecated-internal-metrics)
 1. [`component_received_event_bytes_total` and `component_sent_event_bytes_total` consistently use estimated JSON size of the event](#event_json_size)
 
+and **potentially impactful changes**:
+
+1. [AWS S3 endpoint path changes](#s3-paths)
+
 We cover them below to help you upgrade quickly:
 
 ## Upgrade guide
@@ -61,3 +65,13 @@ of the event should it be serialized to JSON.
 Measuring the events like this allows a consistent measurement to be applied
 across all components regardless of how the source or sink serializes the event
 when connecting to the external service.
+
+### Potentially impactful changes
+
+#### AWS S3 endpoint path changes {#s3-paths}
+
+The handling of AWS S3 endpoints for the `aws_s3` source and sink has changed due to an upgrade of
+the SDK that we use. For S3-compatible APIs like Cloudflare R2 you may find that you need to remove
+the bucket name from the endpoint, if you have it specified. For example
+`https://xxxxxxxxxxxxxxxxxxxxxxxxxxx.r2.cloudflarestorage.com/<bucket name>` should be written as
+`https://xxxxxxxxxxxxxxxxxxxxxxxxxxx.r2.cloudflarestorage.com`.