Fix broken slack messages in Kibana serverless release (#172484)

## Summary
It's the long links we're trying to post to Slack that are breaking the
bot's messaging.

The block build kit says the limit is 3001 characters, we're above that
if we're posting a single "useful links" section, this is why I broke
these up. Tested in
https://buildkite.com/elastic/kibana-serverless-release-1/builds/89 =>
(https://elastic.slack.com/archives/C05NJL80DB8/p1701701355364799)

.buildkite/scripts/serverless/create_deploy_tag/release_wizard_messaging.ts

@@ -366,6 +366,19 @@ async function sendReleaseSlackAnnouncement({
           text:
             '*Useful links:*\n\n' +
             Object.entries(usefulLinksSection)
+              .filter(([name]) => !name.includes('GPCTL'))
+              .map(([name, link]) => ` • <${link}|${name}>`)
+              .join('\n'),
+        },
+      },
+      {
+        type: 'section',
+        text: {
+          type: 'mrkdwn',
+          text:
+            '*GPCTL Dashboards:*\n\n' +
+            Object.entries(usefulLinksSection)
+              .filter(([name]) => name.includes('GPCTL'))
               .map(([name, link]) => ` • <${link}|${name}>`)
               .join('\n'),
         },