Merge pull request #101122 from tmalove/OSDOCS-16684-main

OSDOCS#16684:Add a stub file in 'main' for the 4.21 RNs

Author: skopacz1

release_notes/ocp-4-21-release-notes.adoc

@@ -0,0 +1,11 @@
+:_mod-docs-content-type: ASSEMBLY
+[id="ocp-4-21-release-notes"]
+= {product-title} {product-version} release notes
+include::_attributes/common-attributes.adoc[]
+:context: release-notes
+
+Do not add or edit release notes here. Edit release notes directly in the branch that they are relevant for.
+
+Release note changes should be added or edited in their own PR.
+
+This file is here to allow builds to work.