add SAMPLE_AVG_CPU_LOAD_LIMIT config

[zhyyu]

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Closes #<8773>.
• Update the CHANGES log.

[wu-sheng]

Take a look at how TraceIgnoreExtendService extends from SamplingService. I think it would be more elegant.
This doesn't have to change from the core level.

Another thing is, you add another thread just for CPU usage, which concerns me much. The agent is very sensitive about a new thread. It should be more reasonable to ask JVMService holds the latest CPU value, and provide a method for this new plugin.

[zhyyu]

Take a look at how TraceIgnoreExtendService extends from SamplingService. I think it would be more elegant. This doesn't have to change from the core level.

Another thing is, you add another thread just for CPU usage, which concerns me much. The agent is very sensitive about a new thread. It should be more reasonable to ask JVMService holds the latest CPU value, and provide a method for this new plugin.

Ok, I will try it later using JVMService, add a new plugin like trace-ignore-plugin.

[wu-sheng]

I have commented on the codes, and I think you haven't tried this in the real case, please do so before submitting codes.

[zhyyu]

I have commented on the codes, and I think you haven't tried this in the real case, please do so before submitting codes.

I just used idea to debug the agent code, maybe not production scenario... But it do sent the segment data to OAP. I will change the code according to the comment above.

[wu-sheng]

As you are adding a CPU based sampler, so, you should verify whether this is really working.
The code review only could find out some issues, but can't approve this could work as expected. Also, this plugin doesn't like other plugins, we can't test it automatically.

So, please try to establish a runtime env to verify this plugin.

[wu-sheng]

Any update?

[zhyyu]

Any update?

Recently my work is busy, I will update it when I am free

[zhyyu]

I create a thread run while(true) code, to increase the cpu usage to 15% (124/ 8核)

and then debug the trySampling code

my config is 10% cpu usage limit, 15% cpu usage is above the limit, trySampling return false which meet the expectation.

[wu-sheng]

Please update changes.md and optional plugin doc with agent.config accordingly.