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

configuration/base.yaml

@@ -0,0 +1,9 @@
+application:
+  port: 8000
+  host: 0.0.0.0
+database:
+  host: "localhost"
+  port: 5432
+  username: "postgres"
+  password: "password"
+  database_name: "newsletter"

configuration/local.yaml

@@ -0,0 +1,2 @@
+application:
+  host: 127.0.0.1

configuration/production.yaml

@@ -0,0 +1,2 @@
+application:
+  host: 0.0.0.0