docs: Warn about sendDefaultPii removal (#6156)

Make the upcoming removal visible in the data collection changelog entry
so customers know to migrate before the next major SDK version.

Co-authored-by: Claude <noreply@anthropic.com>

Author: adinauer

CHANGELOG.md

@@ -6,7 +6,11 @@
 
 - Add `LocalSentrySpan` to `sentry-compose` so apps can provide a parent `ISpan` to a composable subtree and have nested `SentryTraced` spans attach to it ([#6112]https://github.com/getsentry/sentry-java/pull/6112)
 - Add `dataCollection`, a fine-grained replacement for `sendDefaultPii`, for controlling data collected automatically by SDK integrations ([#5759](https://github.com/getsentry/sentry-java/pull/5759))
-  - `sendDefaultPii` remains supported for backwards compatibility. When `dataCollection` is not configured, the SDK preserves the existing `sendDefaultPii` behavior.
+
+  > [!WARNING]
+  > `sendDefaultPii` will be removed in the next major SDK version. Migrate to `dataCollection` before upgrading.
+
+  - Until then, when `dataCollection` is not configured, the SDK preserves the existing `sendDefaultPii` behavior.
   - Configuring any `dataCollection` option makes it the source of truth. `sendDefaultPii` is then ignored, and omitted `dataCollection` options use the defaults below.
   - The Logback appender is a compatibility exception. When an encoder is configured, `sendDefaultPii=true` continues to include the original message template and parameters. To opt in independently of `sendDefaultPii`, set `<includeUnencodedMessage>true</includeUnencodedMessage>` on the Sentry appender in `logback.xml` or `logback-spring.xml`.
   - Data explicitly supplied through APIs such as `Sentry.setUser`, scopes, event processors, or `beforeSend` is not affected.