OSDOCS-8463: add build file 4.15 relnotes MicroShift

Author: ShaunaDiaz

microshift_release_notes/microshift-4-15-release-notes.adoc

@@ -0,0 +1,11 @@
+[id="microshift-4-15-release-notes"]
+= {product-title} {product-version} release notes
+include::_attributes/attributes-microshift.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/edited in their own PR.
+
+This file is here to allow builds to work.