[feature][functions] Add the ability to customize logging level for Go & Python functions

[tpiperatgod]

Is your feature request related to a problem? Please describe.
Currently, if the user wants to output more logging level logs other than INFO, it should provide the log settings for different pulsar function runtimes.

Describe the solution you'd like

• Python functions

  Add the --logging_level argument to python_instance_main.py to pass in the logging level, and add the following handle logic to log.py to set the logging level for each handlers.

  def init_logger(level, logfile, logging_config_file):
      global Log
      # get log file location for function instance
      os.environ['LOG_FILE'] = logfile
      logging.config.fileConfig(logging_config_file)
      Log = logging.getLogger()
      # the priority of `level` is higher than `logging_config_file`
      if level != "":
          Log.setLevel(level)
          # set logging level for each handler
          for h in Log.handlers:
              h.setLevel(level)

• Go functions

  Pass in the logging level via environment variable, such as setting LOGGING_LEVEL, then add parsing of the LOGGING_LEVEL environment variable in log.go, , and finally set the logging level.

  const (
  	// environment variable for custom logging level
  	logLevelEnvName      = "LOGGING_LEVEL"
  	defaultLogLevel      = log.InfoLevel
  	defaultLogTimeFormat = "2006/01/02 15:04:05.000"
  )
  
  func init() {
  	log.SetLevel(defaultLogLevel)
  	// lookup and parse the logLevel variable
  	if logLevelStr, exist := os.LookupEnv(logLevelEnvName); exist {
  		if logLevel, err := log.ParseLevel(logLevelStr); err == nil {
  			log.SetLevel(logLevel)
  		}
  	}
  	log.AddHook(&contextHook{})
  	log.SetFormatter(&TextFormatter{})
  }

Describe alternatives you've considered
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Additional context
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