Provide a tool to search for complex relations between messages.

HS-2327492900

## What?
The client would like to find (and get notified about it as well) long-running sessions, where user has not logged out for certain amount of time.
Information about that should be retrieved from messages coming to GL, where single message may contain information about a login or logout.
Effectively, we would need to find latest "logout" and "login" message for each session, per session, perform some calculations on their timestamps and figure out if the session falls into a category of "long-running sessions".

To be more general and not think about specific login/logout/session problem, we may state that some clients may have a need to search for some **relations** between messages stored in the search engine, that cannot be easily expressed with our current search/aggregation capabilities.

The big question is if we can provide a tooling for that, as some general tools implemented by us, capable of retrieving interesting information based on relations between messages?

## Why?
Because we do not provide a clear/easy tool for that, the client has intelligently tried to use pipeline rules with lookup tables to achieve their goal (storing session in lookup table on "login" message and removing it on "logout" message), but because of many problems (please refer to HS ticket for details), it was not possible to achieve it with that method.