Added callout for timestamp logic

Heard from CSM today that our logs weren't showing up because our timestamps were older than 48 hours. Not sure this would have helped, but felt it should be called out.

src/content/docs/logs/log-management/log-api/introduction-log-api.mdx

@@ -328,6 +328,10 @@ Some specific attributes have additional restrictions:
 * `eventType`: Can be a combination of alphanumeric characters, `_` underscores, and `:` colons.
 * `timestamp`: Must be a Unix epoch timestamp. You can define timestamps either in seconds or in milliseconds.
 
+<Callout variant="important">
+  Payloads with timestamps older than 48 hours may be dropped.
+</Callout>
+
 Rate limits on logs sent to the Log API:
 
 * Maximum rate for HTTP requests sent to the Log API: 300,000 requests per minute