feat(pprof): add pprof HTTP server (#807)

- `PPROF_ENABLED=no`
- `PPROF_BLOCK_PROFILE_RATE=0`
- `PPROF_MUTEX_PROFILE_RATE=0`
- `PPROF_HTTP_SERVER_ADDRESS=":6060"`

internal/configuration/sources/env/pprof.go

@@ -0,0 +1,29 @@
+package env
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/qdm12/gluetun/internal/pprof"
+)
+
+func readPprof() (settings pprof.Settings, err error) {
+	settings.Enabled, err = envToBoolPtr("PPROF_ENABLED")
+	if err != nil {
+		return settings, fmt.Errorf("environment variable PPROF_ENABLED: %w", err)
+	}
+
+	settings.BlockProfileRate, err = envToInt("PPROF_BLOCK_PROFILE_RATE")
+	if err != nil {
+		return settings, fmt.Errorf("environment variable PPROF_BLOCK_PROFILE_RATE: %w", err)
+	}
+
+	settings.MutexProfileRate, err = envToInt("PPROF_MUTEX_PROFILE_RATE")
+	if err != nil {
+		return settings, fmt.Errorf("environment variable PPROF_MUTEX_PROFILE_RATE: %w", err)
+	}
+
+	settings.HTTPServer.Address = os.Getenv("PPROF_HTTP_SERVER_ADDRESS")
+
+	return settings, nil
+}