doc: add codenames through to Node.js 34 (2030) (#942)

Extend codenames for a further six releases through to Node.js 34, which takes us to 2030.

By convention, all of our long term support codenames have been chemical elements.

CODENAMES.md

@@ -11,5 +11,11 @@ releases are subject to change.
 * Hydrogen (18.x 2022)
 * Iron (20.x 2023)
 * Jod (22.x 2024)
+* Krypton (24.x 2025)
+* Lithium (26.x 2026)
+* Magnesium (28.x 2027)
+* Neon (30.x 2028)
+* Oxygen (32.x 2029)
+* Platinum (34.x 2030)
 
 The release schedule is available as a [JSON](./schedule.json) file.