copywrite: fix and add copywrite config enterprise comments. (#19590)

Nomad CI checks for copywrite headers using multiple config files
for specific exemption paths. This means the top-level config file
does not take effect when running the copywrite script within
these sub-folders. Exempt files therefore need to be added to the
sub-config files, along with the top level.

demo/.copywrite.hcl

@@ -4,5 +4,9 @@ project {
   license        = "MPL-2.0"
   copyright_year = 2024
 
-  header_ignore = []
+  header_ignore = [
+    // Enterprise files do not fall under the open source licensing. CE-ENT
+    // merge conflicts might happen here, please be sure to put new CE
+    // exceptions above this comment.
+  ]
 }