enable/disable profile at runtime

[localvar]

Easegress could generate CPU & memory profiles for troubleshooting, but this feature can only be enabled from the configuration at startup.

However, some issues only happen after Easegress runs for a long time, if profiling is not enabled at first, it will be very hard to reproduce the issue.

So, we need to add new admin APIs to enable/disable profiles at runtime.

[samutamm]

This would be very useful for debugging memory or cpu issues!

I could work on this. The API could be following:

Path	Method	Description	Data
/profile/	GET	Get info of current CPU & memory profiling. For example, whether enabled and what's the path to file.	-
/profile/start/cpu	POST	Start profiling CPU to given file.	Path for CPU profile file.
/profile/stop/cpu	POST	Stops profiling and dumps the results to file.	-
/profile/start/memory	POST	Start profiling memory to given file.	Path to Memory profile file.
/profile/stop/memory	POST	Stop profiling and dumps results to file.	-

The profiling logic already exists in https://github.com/megaease/easegress/blob/main/pkg/profile/profile.go and the endpoint methods above could use it to start and stop profiling.