ref(spans): Warn about experimental attachments (#15804)

Author: jjbayer

develop-docs/sdk/data-model/envelope-items.mdx

@@ -115,6 +115,10 @@ file. It is always associated to an event or transaction.
 
 ### Trace Attachment
 
+<Alert level="warning">
+Trace attachments are an experimental feature that is still under development.
+</Alert>
+
 Item type `"attachment"` with content type `"application/vnd.sentry.trace-attachment"`. This item contains a raw payload of an attachment together with metadata. Contrary to V1 attachments, trace attachments are only optionally associated with other trace items (spans, logs, ...). Their main association is with the trace itself.
 
 **Envelope Headers:**

develop-docs/sdk/telemetry/spans/span-protocol.mdx

@@ -218,6 +218,10 @@ span_id: "438f40bd3b4a41ee"
 
 ## Span Attachments
 
+<Alert level="warning">
+Span attachments are an experimental feature that is still under development.
+</Alert>
+
 To associate an attachment with a span, submit a [trace attachment](/sdk/data-model/envelope-items/#trace-attachment) item with an additional `span_id` item header. The trace attachment _should_ be submitted in the same envelope as the span itself.
 
 - `span_id` is the ID of the span that owns the attachment. If set, the attachment will be dropped with the span if the span is dropped by dynamic sampling, inbound filters or rate limits. That is, Relay treats `span_id` as the owner of the attachment.