Support ALTER ROUTINE LOAD JOB stmt, for example:
```
alter routine load db1.label1
properties
(
"desired_concurrent_number"="3",
"max_batch_interval" = "5",
"max_batch_rows" = "300000",
"max_batch_size" = "209715200",
"strict_mode" = "false",
"timezone" = "+08:00"
)
```
Details can be found in `alter-routine-load.md`
Stream load should read all the data completely before parsing the json.
And also add a new BE config streaming_load_max_batch_read_mb
to limit the data size when loading json data.
Fix the bug of loading empty json array []
Add doc to explain some certain case of loading json format data.
Fix: #4124
This CL mainly changes:
1. Reorganized the code logic to limit the supported json format to two, and the import behavior is more consistent.
2. Modified the statistical behavior of the number of error rows when loading in json format, so that the error rows can be counted correctly.
3. See `load-json-format.md` to get details of loading json format.
