feat: Add fgprof debug endpoint for Off-CPU time analysis

[dongjiang1989]

Add fgprof debug endpoint for Off-CPU time analysis.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: dongjiang1989
Once this PR has been reviewed and has the lgtm label, please assign justinsb for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[netlify]

✅ Deploy Preview for agent-sandbox canceled.

Name	Link
🔨 Latest commit	4a0d0a4
🔍 Latest deploy log	https://app.netlify.com/projects/agent-sandbox/deploys/69d23c5738195300084404f4

[barney-s]

Its a single maintainer profiler that exposes significant information.
Wondering if we need a separate flag to guard it.

@justinsb FYI

[justinsb]

Yeah, it's a good question. It is MIT licensed, and it does look to have been updated recently, so I think abandonment risk is low. I think if we hid this behind a go build tag, then it would be very easy to accept. Behind a flag would also work. My biggest concern is that we accidentally consider this part of our "feature set" and then we can never remove it, even if go implements something similar. And it does seem like a good feature, so I both want it in this library and I imagine go might one day add it!

@dongjiang1989 WDYT - is this something we should ship to everyone? Or is it more like the race detector ( #331 ) where we want to enable it in our CI but it's not as valuable for end-users?

[dongjiang1989]

Yeah, it's a good question. It is MIT licensed, and it does look to have been updated recently, so I think abandonment risk is low. I think if we hid this behind a go build tag, then it would be very easy to accept. Behind a flag would also work. My biggest concern is that we accidentally consider this part of our "feature set" and then we can never remove it, even if go implements something similar. And it does seem like a good feature, so I both want it in this library and I imagine go might one day add it!

@dongjiang1989 WDYT - is this something we should ship to everyone? Or is it more like the race detector ( #331 ) where we want to enable it in our CI but it's not as valuable for end-users?

Thanks @justinsb @barney-s
fgprof acts as a complementary enhancement to the native Go pprof. It can be exposed to users for debugging purposes — users can capture related profiling information when troubleshooting and attaching it to issues.
That said, I suggest keeping this feature disabled by default.