In the past, when we want to modify some BE configs, we have to modify be.conf and then restart BE.
This patch provides a way to modify configs in the type of 'threshold', 'interval', 'enable flag'
when BE is running without restarting it.
You can update a single config once by BE's http API: `be_host:be_http_port/api/update_config?config_name=new_value`
Class definition of ByteBuffer duplicates between olap/byte_buffer.h and util/byte_buffer.h.
All of the two classes has a function names as remaining().
Some place which want to call remaining() of util/byte_buffer.h is linked to the other remaining() function of olap/byte_buffer.h
