Initial exercise setup.

Additions

* Instructions for manually starting the database.
* Each phase now has a success criteria with how to verify.
* Troubleshooting section for working with the Docker DB container.
* All phases of the exercise are described in README.md (with as little advanced hints as possible).
* DFD to illustrate phase 1
* Debugging starts the database container and applies schema migrations (no setup required).
* Launch settings for VS Code, VS 2022 and Rider (IntelliJ IDEA).
* Swagger UI is available at <http://localhost:8080/swagger/index.html> for testing.

dbschemas/01-create-posts-table.sql

@@ -0,0 +1,7 @@
+-- Schema generated from this sample: https://jsonplaceholder.typicode.com/posts/1
+CREATE TABLE posts (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER NOT NULL,
+    title TEXT NOT NULL,
+    body TEXT NOT NULL
+);