feat(api): containerization

- 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

Dockerfile.production

@@ -0,0 +1,20 @@
+# We use the latest Rust stable release as base image
+FROM rust:1.78.0
+# Let's switch our working directory to `app` (equivalent to `cd app`)
+# The `app` folder will be created for us by Docker in case it does not
+# exist already.
+WORKDIR /app
+# Install the required system dependencies for our linking configuration
+RUN apt update && apt install lld clang -y
+
+# Copy all files from our working environment to our Docker image
+COPY . .
+# Let's build our binary!
+# We'll use the release profile to make it faaaast
+ENV SQLX_OFFLINE true
+RUN cargo build --release
+
+ENV APP_ENVIRONMENT production
+
+# When `docker run` is executed, launch the binary!
+ENTRYPOINT ["./target/release/email_newsletter_api"]