Allow array of files for dupeclassescheck_ignorelist

[plaird]

We can't break back compat, so create a new attribute dupeclassescheck_ignorelists (s on end) that takes an array. This is useful when there are common ignores shared by many projects, but also service specific ignores.

   dupeclassescheck_ignorelists = [
      "//common/boot/dupe_ignores.txt",
      "dupeclasses.txt",
   ]