Support login session, query payload, and multi events

[ryli17]

This PR is to resolve the following issues:

1. Authentication through another path For example, login through http://1.1.1.1/login, but query through http://1.1.1.1/query. After successfully logged in, session information is exchanged by cookies.
2. Each query may return multiple items. For example, one query may return a json object, such as {"entries":[{"message": "message 1"}, {"message":"message 2"}]}. The expected fluentd output is 2020-09-01 12:00:00 tag: {"message":"message 1"} 2020-09-01 12:00:00 tag: {"message":"message 2"}

Detailed usage please refer to README