Changes to datetime formatting

[bazay]

Formatting a datetime should only pertain to itself and valid datetimes do not contain a space. Should there be a desire to show show a space between the datetime and the process pid in the formatted log, this formatting logic should take place there.
Furthermore, the default datetime format is moved to a class variable to allowing this variable to be overwritten by subclasses.

[bazay]

I wrote a formatter for my ruby logger, inheriting from Logger::Formatter, where its responsibility was to format logs to JSON.
Within the json serialization process, I had a field for time which basically works to the following effect:

class MyFormatter < Logger::Formatter
  def call(severity, datetime, progname, message)
    { severity: severity, datetime: format_datetime(datetime), progname: progname, message: message }.to_json
  end
end

MyFormatter.new.call('INFO', Time.now, nil, 'Test logger')
#=> {"severity":"INFO","datetime":"2021-07-29T09:15:48.031718 ","progname": null,"message":"Test logger"} 

Notice the trailing space for the value of datetime.
In order to remove that space with the current code a developer would need to call #strip on the result of format_datetime(datetime) which seems like an oversight, as this is something that should be handled by the default logger code in my humble opinion.

[luisdavim]

LGTM 👍

[hsbt]

@bazay Can you add new test-case about this change?

[bazay]

@hsbt Added test cases

[bazay]

Bump @hsbt @luisdavim 🙃

[bazay]

Bump @hsbt @luisdavim :)