runtime/pprof,runtime: add new goroutine leak profile as a GOEXPERIMENT

[mknyszek]

This is a mini-proposal to land the work powering #74609 behind a new GOEXPERIMENT, goleakprofile, so

1. The implementation CL can stop accumulating merge conflicts,
2. More people can try it out.

RE: (2), I think we actually already have a substantial amount of evidence that this is widely applicable. The extensive test suite added in https://go.dev/cl/688335 includes minimized versions of real leaks found in real-world large scale Go programs in the wild. The main reason here is (1).

[gabyhelp]

Related Issues

• proposal: runtime/pprof,runtime: new goroutine leak profile #74609

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[aclements]

Let's call it GOEXPERIMENT=goroutineleakprofile to match the name of the profile and drop the "r" on the end.

[mknyszek]

Done, renamed in the proposal issue, and send a comment on the CL to update the name.

[aclements]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— aclements for the proposal review group