[Filebeat] Add module for AWS S3 server access log

[kaiyan-sheng]

This module is to parse S3 server access logs that are retrieved by s3 input. Please see https://docs.aws.amazon.com/AmazonS3/latest/dev/LogFormat.html for more details on S3 server access log format.

closes #12880

How to test this:

1. Setup S3 bucket and SQS notification: https://docs.aws.amazon.com/AmazonS3/latest/dev/ways-to-add-notification-config-to-bucket.html#step1-create-sqs-queue-for-notification
2. Pull this PR(if it's not merged) and build a new filebeat binary under x-pack:
   kaiyansheng@KaiyanMacBookPro:~/go/src/github.com/elastic/beats/x-pack/filebeat (s3_access_log)$ mage update; mage build
3. Enable aws module:
   kaiyansheng@KaiyanMacBookPro:~/go/src/github.com/elastic/beats/x-pack/filebeat (s3_access_log)$ ./filebeat modules enable aws
4. Update aws.yml with SQS url and AWS credentials:

- module: aws
  s3access:
    enabled: true

    # AWS SQS queue url
    var.queue_url: https://sqs.ap-southeast-1.amazonaws.com/123/test-s3-notification

    # Profile name for aws credential
    var.credential_profile_name: test-mb

5. Disable filebeat default log input in filebeat.yml by comment out the part in below:

filebeat.inputs:

# Each - is an input. Most options can be set at the input level, so
# you can use different inputs for various configurations.
# Below are the input specific configurations.

- type: log

  # Change to true to enable this input configuration.
  enabled: false

  # Paths that should be crawled and fetched. Glob based paths.
  paths:
    - /var/log/*.log

6. Start metricbeat with ./metricbeat -e

[kaiyan-sheng]

jenkins, test this please

[kaiyan-sheng]

jenkins, test this please