This patch supports utf8mb4 for mysql external table.
if someone needs a mysql external table with utf8mb4 charset, but only support charset utf8 right now.
When create mysql external table, it can add an optional propertiy "charset" which can set character fom mysql connection,
default value is "utf8". You can set "utf8mb4" instead of "utf8" when you need.
1. replace all boost::shared_ptr to std::shared_ptr
2. replace all boost::scopted_ptr to std::unique_ptr
3. replace all boost::scoped_array to std::unique<T[]>
4. replace all boost:thread to std::thread
1. Fix bug of UNKNOWN Operation Type 91
2. Support using resource_tag property of user to limit the usage of BE
3. Add new FE config `disable_tablet_scheduler` to disable tablet scheduler.
4. Add documents for resource tag.
5. Modify the default value of FE config `default_db_data_quota_bytes` to 1PB.
6. Add a new BE config `disable_compaction_trace_log` to disable the trace log of compaction time cost.
7. Modify the default value of BE config `remote_storage_read_buffer_mb` to 16MB
8. Fix `show backends` results error
9. Add new BE config `external_table_connect_timeout_sec` to set the timeout when connecting to odbc and mysql table.
10. Modify issue template to enable blank issue, for release note or other specific usage.
11. Fix a bug in alpha_row_set split_range() function.
At present, the application of vlog in the code is quite confusing.
It is inherited from impala VLOG_XX format, and there is also VLOG(number) format.
VLOG(number) format does not have a unified specification, so this pr standardizes the use of VLOG
1. Support limit clause push down both odbc table and mysql table.
2. Code refactor of ODBC Scan Node, change `build_connect_string` and `query_string` from BE to FE to make it easily to modify
