[dartdoc] Add header and footer options to dartdoc options

Bug: b/323126451
Cq-Include-Trybots: luci.dart.try:dart-sdk-linux-try
Change-Id: Iedc6a4d282da3beae7bdcf522c4ae0bab8644a3c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/354886
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>

tools/write_dartdoc_options_file.py

@@ -78,6 +78,12 @@ def Main(argv):
     - unknown-file
     - unknown-macro
     - unresolved-doc-reference
+  header:
+    - ../../../tools/bots/dartdoc_header.html
+  footer:
+    - ../../../tools/bots/dartdoc_footer.html
+  footerText:
+    - ../../../tools/bots/dartdoc_footer_text.html
 ''' % revision
     with open(args.output, 'w') as f:
         f.write(output)