Add shared types module

[Mackenzie-OO7]

Closes #12

Note

• Compilation kept failing because soroban_sdk::crypto::Client::sha256 strictly requires soroban_sdk::Bytes, but got passed soroban_sdk::Vec<u8>. These types are not interchangeable in the Soroban environment so i refactored authorixation.rs a bit

• I created a root cargo workspace for all the contract directories to share so they can easily use relative paths

[phertyameen]

Your cicd is failing:
run

cargo clippy 
cargo build

in the affected contract directory to resolve contract test errors

[phertyameen]

Awsome work!