Add file rolling function in file sink.

[youyongsong]

Background

I known File Sink is currently mostly used in local development, but we also tend to use it in our production environment with fluentd, because this combination is very stable and reliable.

Currently File Sink lacks the file rolling function, which is very important for the production environment. So I want to add file rolling function to File Sink through this pr without breaking changes.

Usage

file rolling is disabled by default, and can be enabled by adding the following arguments:

- receivers:
  file:
    path: ./test.log
    maxsize: 20    // if ./test.log is larger than 20MB, it will be renamed to ./test-<datetime>.log as a backup file,
    and create a new file named test.log to receive events. It defaults to 100 megabytes.
    maxage: 20     // if backup files ./test-<datetime>.log are created 20 days ago, they will be deleted. The default
    is not to remove old log files based on age.
    maxbackups: 3  // if backup files are more than 3, older backup files will be removed.

the rolling function is powered by lumberjack. Becasue lumberjack.Logger implmented io.WriteCloser interface, so it is easy to replace file *os.file with writer &lumberjack.Logger.

Test Result

run kubernetes-event-exporter with following config:

logLevel: debug
route:
  match:
    - receiver: "file"
receivers:
  - name: "file"
    file:
      path: "./event.log"
      maxsize: 1
      maxbackups: 4

run following script to generate events and output ./event*.log status:

while true
do
  kubectl run nginx --image nginx || kubectl delete deployment nginx
  ls -lh event*.log
  sleep 2
done

the result is:

deployment.apps "nginx" deleted
-rw-r--r-- 1 ysyou staff  1.0M Mar  4 18:03 event-2020-03-04T10-03-30.271.log
-rw-r--r-- 1 ysyou staff  1.0M Mar  4 18:15 event-2020-03-04T10-15-52.496.log
-rw-r--r-- 1 ysyou staff  1.0M Mar  4 18:28 event-2020-03-04T10-28-27.334.log
-rw-r--r-- 1 ysyou staff  1.0M Mar  4 18:41 event-2020-03-04T10-41-11.316.log
-rw-r--r-- 1 ysyou staff 1023K Mar  4 18:54 event.log
deployment.apps/nginx created
-rw-r--r-- 1 ysyou staff 1.0M Mar  4 18:15 event-2020-03-04T10-15-52.496.log
-rw-r--r-- 1 ysyou staff 1.0M Mar  4 18:28 event-2020-03-04T10-28-27.334.log
-rw-r--r-- 1 ysyou staff 1.0M Mar  4 18:41 event-2020-03-04T10-41-11.316.log
-rw-r--r-- 1 ysyou staff 1.0M Mar  4 18:54 event-2020-03-04T10-54-11.451.log
-rw-r--r-- 1 ysyou staff 2.0K Mar  4 18:54 event.log

when event.log reaches 1M, it is renamed to event-2020-03-04T10-54-11.451.log, because backup files are more than 4, the oldest one event-2020-03-04T10-03-30.271.log is deleted.

[youyongsong]

hi @mustafaakin , please help review this pr~