ddl: Fix ddl owner doesn't use etcd keyspace prefix

[djshow832]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:
#57179 updates the order of setting etcdcli key prefix and creating ddl owner manager. After the change, the etcdcli of ddl owner manager doesn't have the keyspace prefix.
When bootstrapping, the DDL owner is occupied by another TiDB and this TiDB keeps in the loop of bootstrap.

What changed and how does it work?

Set the prefix before creating the ddl owner.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

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None

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[djshow832]

The PR to the master: #60403