Add banner for 8.1 RC (#213)

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### Issues Resolved

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- [x] Commits are signed per the DCO using `--signoff`

By submitting this pull request, I confirm that my contribution is made
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---------

Signed-off-by: Nigel Brown <[email protected]>
Signed-off-by: Madelyn Olson <[email protected]>
Co-authored-by: Madelyn Olson <[email protected]>

Author: pnbrown

config.toml

@@ -49,3 +49,6 @@ publish_hold = [
     "/topics/internals/",
     "/topics/rdd/"
 ]
+
+banner = "Valkey 8.1 is generally available! [Check it out](https://valkey.io/download/releases/v8-1-0/)"
+