Create examples dir to showcase GCT features

[thrasher-]

To make it easier for people to get started with GCT, we should create a consolidated examples directory that showcases all the different ways users can achieve their trading goals using the platform. This directory should include examples of gctscript, engine/gRPC, backtester and library usage. One of the most common questions people ask is how they can get started writing or using a strategy, despite existing examples in each of these subsystems.

A mock dir structure could be something like:

examples/
    gctscript/
    engine/
    lib/
    backtester/
    README.md

The README.md file would contain a table of supported strategies and instructions on how to run each example for each subsystem.