br block on create policy

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

br restore requires tidb Domain started to do ddls. after #54913 we have separate domain Init and Start, br should start it explicitly.

2. What did you expect to see? (Required)

success

3. What did you see instead (Required)

block on running ddl

4. What is your TiDB version? (Required)

master