[Bug] After the coordinator restarts, the user field will be lost in heartbeat

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/incubator-uniffle/issues?q=is%3Aissue) and found no similar issues.

### Describe the bug

The user field will only be present during the registration process of RssShuffleManager, if Coordinator restarts, the user will be lost.

### Affects Version(s)

master

### Uniffle Server Log Output

_No response_

### Uniffle Engine Log Output

_No response_

### Uniffle Server Configurations

_No response_

### Uniffle Engine Configurations

_No response_

### Additional context

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

Start with the RssShuffleManager registration and Coordinator heartbeat paths named in the report, then trace how the user field is carried before and after a Coordinator restart. Done means the user field remains present in heartbeat messages after restart, with a regression test covering that scenario.

Written by the indexing model from the issue text.