TiCDC get changefeeds api does not work well.

[asddongmen]

What did you do?

0. start a cdc server
1. create a changefeed named "test1"
2. pause changefeed "test1"
3. kill and restart cdc server
   4.curl -X GET "http://127.0.0.1:8300/api/v1/changefeeds/test1"

What did you expect to see?

{
    "namespace": "default",
    "id": "test1",
    "sink_uri": "blackhole://",
    "create_time": "2022-06-13 10:04:55.204",
    "start_ts": 433870836907376641,
    "resolved_ts": 433870842556317698,
    "target_ts": 0,
    "checkpoint_tso": 433870842294173698,
    "checkpoint_time": "2022-06-13 10:05:15.734",
    "sort_engine": "unified",
    "state": "normal",
    "error": null,
    "error_history": null,
    "creator_version": "",
    "task_status": [ ]
}%

### What did you see instead?

```log
{
    "error_msg": "[CDC:ErrChangeFeedNotExists]changefeed not exists, {default test1}",
    "error_code": "CDC:ErrChangeFeedNotExists"
}%

### Versions of the cluster

Upstream TiDB cluster version (execute `SELECT tidb_version();` in a MySQL client):

```console
(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

master branch