Explain the changes

1. Change printing of Warning stuck buffer_pool buffer from console.warn to console.error.

Issues:

1. Related to issue Error: Warning stuck buffer_pool buffer with IO workload  #8521 when the buffer gets timeout (after 2 minutes by current configuration) it prints an error in logs, although the operation is not failing, and all the names are related to warning: warning_timer, Warning stuck buffer_pool buffer, this.warning_timeout, therefore changing it in the logs to WARN instead of ERROR.

Testing Instructions:

1. none (if you want to reproduce it with code changes please see comment).

• Doc added/updated
• Tests added