Profiling: Add base, fix memory profiling (#8850)

For 'snapshot' type profiles, record a 'before' profile that can be used 
as `go tool pprof -base=before ...` to compare before and after.

"Before" profiles are included in the zipped package.

[`runtime.MemProfileRate`](https://golang.org/pkg/runtime/#pkg-variables) 
should not be updated while the application is running, so we set it at startup.

Co-authored-by: Harshavardhana <harsha@minio.io>

cmd/server-main.go

@@ -255,6 +255,7 @@ func serverMain(ctx *cli.Context) {
 	if ctx.Args().First() == "help" || !endpointsPresent(ctx) {
 		cli.ShowCommandHelpAndExit(ctx, "server", 1)
 	}
+	setDefaultProfilerRates()
 
 	// Initialize globalConsoleSys system
 	globalConsoleSys = NewConsoleLogger(context.Background())