Wiki Find Page to opt_out

Closes https://gitlab.com/gitlab-org/gitaly/issues/894

changelogs/unreleased/zj-wiki-find-file-opt-out.yml

+---
+title: Finding a wiki page is done by Gitaly by default
+merge_request:
+author:
+type: other

lib/gitlab/git/wiki.rb

@@ -67,7 +67,8 @@ module Gitlab
       end
       def page(title:, version: nil, dir: nil)
-        @repository.gitaly_migrate(:wiki_find_page) do |is_enabled|
+        @repository.gitaly_migrate(:wiki_find_page,
+                      status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |is_enabled|
           if is_enabled
             gitaly_find_page(title: title, version: version, dir: dir)
           else