[BUG] format of filter logs' date is not RFC3339

[frikilax]

Describe the bug
Darwin should be consistent when using date formats in alerts, manager and filters' logs .
However, this is currently not the case:

• date format in manager logs : 2020-07-22 13:22:53,750 (not correct)
• date format in filters logs: Fri Jun 5 15:00:01 2020 (not correct)
• date format in alerting: 2020-09-07T11:58:35Z

Plateform (please complete the following information):

• OS (version): Ubuntu 18.04/HBSD12-STABLE
• Darwin version: 1.3.1

To Reproduce
Steps to reproduce the behavior:

1. Change manager configuration to DEBUG (in service file)
2. Setup a darwin configuration with at least a filter in DEBUG
3. Start darwin and ensure filter is started
4. check darwin_manager.log and darwin.log
5. formats should be different

Expected behavior
All date formats should be consistent between sources, adn preferably valid and consistent RFC3339 (%Y%Y%Y%Y-%M%M-%D%DT%h%h:%m%m:%s%sZ)

Screenshots/logs
date log format for darwin.log (filters' logs):

date log format for darwin_manager.log (manager's logs):

(preferred) date log format for alerts.Log: