- Build SQLx queries beforehand so that we don't have to do PostgreSQL
init right away at service start up
- Created `Dockerfile.production`
- Updated docs
- Seperate configuration files for local and development environments
- Added `serde` crate for serialisation or deserialisation of data
- Added test cases for the `subscribe` API route
- Refactor the testing setup to another module `test_utils`
- use random TCP port for testing