Consider only output to LOG instead of hardcoded stdout/stderr

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/incubator-kvrocks/issues) and found no similar issues.

### Motivation

Refer to https://github.com/apache/incubator-kvrocks/pull/660#issuecomment-1165637383.

It is good to keep kvrocks with only one output location.
But currently, kvrocks also outputs some information to stdout when logdir is set to a regular file, which can be confusing for users.

### Solution

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by reading the linked pull request comment and tracing how logdir set to a regular file is handled. Identify the paths that write to stdout or stderr instead of LOG, then define done as routing those messages to the single configured output location and verify the behavior with relevant logging tests.

Written by the indexing model from the issue text.