Add a JSON format for existing metrics like this.
```
{
"tags":
{
"metric":"thread_pool",
"name":"thrift-server-pool",
"type":"active_thread_num"
},
"unit":"number",
"value":3
}
```
I add a new JsonMetricVisitor to handle the transformation.
It's not to modify existing PrometheusMetricVisitor and SimpleCoreMetricVisitor.
Also I add
1. A unit item to indicate the metric better
2. Cloning tablet statistics divided by database.
3. Use white space to replace newline in audit.log
Fix some unittest failed due to glog， this may be we change the ut build dir，and the log path is not exist in new build dir， so we change the log from file to stdout
* Enhence the usabilities
1. Add metrics to monitor transactions and steaming load process in BE.
2. Modify BE config 'result_buffer_cancelled_interval_time' to 300s.
3. Modify FE config 'enable_metric_calculator' to true.
4. Add more log for tracing broker load process.
5. Modify the query report process, to cancel query immediately if some instance failed.
* Fix bugs
1. Avoid NullPointer when enabling colocation join with broker load
2. Return immediately when pull load task coordinator execution failed
Added: Support getting column size and precision info of table or view using JDBC.
Updated: Change the promethues type name GAUGE to lowercase, to fit the latest promethues version.
Updated: Backend ip saved in FE will be compared with BE's local ip when doing heartbeat, to avoid false positive heartbeat response.
Updated: Using version_num of tablet instead of calculating nice value to select cumulative compaction candicates.
Fixed: Predicates should not be pushed down to subquery which contains limit clause.
Fixed: Fix the formula of calculating BE load score.
Fixed: Fix a bug that in some edge cases, non-master Fontend may wait for a unnecessary long timeout after forwarding cmd to Master FE.
Fixed: A bug that granting privs on more than one table does not work.
Fixed: Support 'Insert into' table which contains HLL columns.
Fixed: ExportStmt' toSql() method may throw NullPointer Exception if table does not exist.
Fixed: Remove unnecessary 'get capacity' operation to avoid IO impact.
Internal commit id: merge to c16bd603a53dfe2089ff95704c698a738c317792
