log: support maxBackups in config.toml

[zlacfzy]

Description

Add maxBackups in config.toml.
MaxBackups means the log file that would be retained, by default it would be 0, which means there is no limitation.
If set MaxBackups = 240, only logs of the most recent 240 hours(10 days) would be kept, since the default rotate time is 1 hour.
See more: #2165.

Rationale

Add a MaxBackups in Node.LogConfig.

[Node.LogConfig]
FileRoot = ""
FilePath = "bsc.log"
MaxBytesSize = 10485760
Level = "info"

Example

[Node.LogConfig]
FileRoot = ""
FilePath = "bsc.log"
MaxBytesSize = 10485760
Level = "info"
MaxBackups = 240

Changes

Notable changes:

• log: add maxBackups in config.toml

[zzzckck]

I would prefer: remove the specified 1 log file on rotateFile()
like:

func (w *AsyncFileWriter) rotateFile() {
	select {
	case <-w.timeTicker.C:
		if err := w.flushAndClose(); err != nil {
			fmt.Fprintf(os.Stderr, "flush and close file error. err=%s", err)
		}
		if err := w.initLogFile(); err != nil {
			fmt.Fprintf(os.Stderr, "init log file error. err=%s", err)
		}
                // start from here
                if maxBackups > 0 {
		   if err := w.removeExpiredFile(); err != nil {
			fmt.Fprintf(os.Stderr, "remove expired file error. err=%s", err)
		   }
                }
                // end
	default:
	}
}