add data subsystem

[jondot]

No description provided.

[kaplanelad]

Hey Dotan, fow notes:

1. When generating data getting this error

❯ cargo loco generate data test
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 4.21s
     Running `target/debug/myapp-cli generate data test`
added: "data/test/data.json"
added: "src/data/test.rs"
Error: Generators(RRgen(Message("cannot inject into src/data/mod.rs: file does not exist")))

2. Adding generator tests here