A race condition in ConfigManager

```java
// Multiple of these callables can be submitted at the same time, but the callables themselves
// are executed serially, so double check that it hasn't already been populated.
if (!watchedConfigs.containsKey(key)) {
byte[] value = dbConnector.lookup(configTable, "name", "payload", key);
ConfigHolder holder = new ConfigHolder(value, serde);
watchedConfigs.put(key, holder);
}
```

Start by locating ConfigManager and the code around watchedConfigs, then trace how multiple callables reach the dbConnector lookup. Determine how concurrent calls can populate the same key more than once; done means the race is prevented without breaking configuration loading.

Written by the indexing model from the issue text.