Prepare release candidate for 1.21 (#7349)

Author: friedrichg

RELEASE.md

@@ -36,7 +36,7 @@ Our goal is to provide a new minor release every 6 weeks. This is a new process
 | v1.18.0        | 2024-08-16                                 | Daniel Blando (@danielblando)               |
 | v1.19.0        | 2025-01-22                                 | Charlie Le (@charlietle)                    |
 | v1.20.0        | 2025-10-31                                 | Ben Ye (@yeya24)                            |
-| v1.21.0        | 2026-03-09                                 | Friedrich Gonzalez (@friedrichg)            |
+| v1.21.0        | 2026-03-12                                 | Friedrich Gonzalez (@friedrichg)            |
 
 ## Release shepherd responsibilities
 

VERSION

@@ -1 +1 @@
-1.20.1
+1.21.0-rc.0