Rework `spacetime init` to use a standardized templates folder

[cloutiertyler]

We want to host all module examples at the root of the SpacetimeDB repo with the following structure:

templates
  quickstart-chat-ts
    spacetimedb  
  quickstart-chat-rs
    spacetimedb
  quickstart-chat-cs
    spacetimedb
  blackholio-unreal
    spacetimedb
  blackholio-unity
    spacetimedb

And then spacetime init should just use these directly. This requires fixing CI which will break if we do this