Add plots for new 1.26 metrics

[arl]

New metrics:

• /sched/pauses/stopping/gc:seconds float64histogram. Add plots for Go 1.26 scheduler pause metrics #140
• /sched/pauses/stopping/other:seconds float64histogram. Add plots for Go 1.26 scheduler pause metrics #140
• /sched/pauses/total/gc:seconds float64histogram. Add plots for Go 1.26 scheduler pause metrics #140
• /sched/pauses/total/other:seconds float64histogram. Add plots for Go 1.26 scheduler pause metrics #140
• /sched/goroutines-created:goroutines uint64 internal/plots: refactor + add new go1.26 plots #142
• /sched/goroutines/not-in-go:goroutines uint64 internal/plots: refactor + add new go1.26 plots #142
• /sched/goroutines/runnable:goroutines uint64 internal/plots: refactor + add new go1.26 plots #142
• /sched/goroutines/running:goroutines uint64 internal/plots: refactor + add new go1.26 plots #142
• /sched/goroutines/waiting:goroutines uint64 internal/plots: refactor + add new go1.26 plots #142
• /sched/threads/total:threads uint64 internal/plots: refactor + add new go1.26 plots #142
• /gc/cleanups/executed:cleanups uint64 1.26/cleanup finalizer queues #143
• /gc/cleanups/queued:cleanups uint64 1.26/cleanup finalizer queues #143
• /gc/finalizers/executed:finalizers uint64 1.26/cleanup finalizer queues #143
• /gc/finalizers/queued:finalizers uint64 1.26/cleanup finalizer queues #143

See #golang/go/issues/15490 for /sched/pauses/

The following are less useful, so not doing them now.

• /gc/gogc:percent uint64
• /gc/heap/tiny/allocs:objects uint64
• /gc/limiter/last-enabled:gc-cycle uint64
• /gc/scan/total:bytes uint64