Avoid creating command topic when backup file exists

[stevenpyzhang]

Is your feature request related to a problem? Please describe.
If the command topic is deleted when backups are enabled, and then the server is restarted, the command topic gets recreated even though a backup file exists. The server will most likely immediately enter a DEGRADED state due to the backup not matching the newly created command topic

Describe the solution you'd like
As part of startup, we could avoid creating the command topic if the backup file is enabled and the server detects a backup file exists.

Additional context
In KsqlRestApplication

  private void registerCommandTopic() {

    final String commandTopic = commandStore.getCommandTopicName();

    KsqlInternalTopicUtils.ensureTopic(
        commandTopic,
        ksqlConfigNoPort,
        serviceContext.getTopicClient()
    );
...

Ensure topic doesn't check to see if backups are enabled or if a backup file exists already, so it'll just always create a command topic when the server starts up and the broker doesn't have a command topic.