Tracee plugins

[yanivagman]

We recently added support for signature plugins to Tracee-rules.
There are several other use cases for which we should consider adding plugins support:

1. Processor plugins - these plugins can process the output of tracee, and produce different insights. For example, building the process tree (using fork and exec syscalls), open files table, connected sockets and so on. This processed data can then be an input for different signatures that can use it without having to build the state on their own.
2. eBPF program plugins - these plugins can extend the functionality of Tracee by hooking programs given by the user to a chosen probe. The output emitted by these programs can then be displayed as any other Tracee event.