chore: Update reviewers for OpenAPI repo to use APIx Platform team name (#958)

Author: matt-condon

.github/CODEOWNERS

@@ -1,6 +1,6 @@
 # Maintained by the APIx team
-*                         @mongodb/apix
-/tools/cli/               @mongodb/apix-2 @mongodb/apix1
-/tools/spectral/ipa/      @mongodb/apix1
-/tools/postman/           @mongodb/apix1
-package.json              @mongodb/apix1
+*                         @mongodb/apix-platform
+/tools/cli/               @mongodb/apix-platform
+/tools/spectral/ipa/      @mongodb/apix-platform
+/tools/postman/           @mongodb/apix-platform
+package.json              @mongodb/apix-platform