[Bug] BE Memory Leak In Json Load

[stdpain]

Describe the bug
BE Memory Leak

To Reproduce
Steps to reproduce the behavior:

1. Create a Table
2. Using JSON load multiple times
3. Memory increased from 400M to 3G in 20 mins
4. when i stop json load, mem will stay at 2G
5. I use tcmalloc heap profile，I found a memory leak at StreamLoadPipe::read_one_message

Screenshots
Here is the HEAP_PROFILE

I Found the leak Here and run the profile again

So I want to use smart pointers to refactor this code

[HappenLee]

@stdpain It's a good time to refactor this part of the code to use unique_ptr avoid the use of the raw pointer.