chore(dynamic-sampling): add notice that we will remove the get samples button (#15710)

- As we will be removing the Get Samples button as part of our move to
Span First, we want to shout this out in the docs

Closes TET-1479

Author: shellmayr

docs/organization/dynamic-sampling/index.mdx

@@ -206,6 +206,10 @@ We deprioritize health check type transactions because while they're important f
 
 ### Get Samples
 
+<Alert>
+The "Get Samples" button and the investigation rules that go along with it will be retired in Spring 2026. From that point on, you will no longer be able to create new investigation rules.
+</Alert>
+
 Our automated dynamic sampling priorities work well in a generic manner to collect a baseline of samples because they prioritize retaining data that's valuable for any customer at any given time. However, there are certain scenarios, such as investigating a particular issue, when very specific data becomes temporarily more important. In such cases, the automated sampling priorities may not provide enough samples, so you may want to create investigation rules.
 
 Investigation rules are sampling rules that can be created through the Sentry UI to temporarily boost the number of events collected for a particular scenario (for example, events with specific tag values). These rules can be created to retain more samples when too few (less than 5) are available. Once created, a rule will be active for up to 48 hours or until 100 samples are collected. You'll be notified via email when enough events have been collected.