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.

Dockerfile

@@ -0,0 +1,8 @@
+# Normally, we would use a multi-stage build, but for simplicity, we are using a single stage here.
+FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
+WORKDIR /src
+COPY . .
+RUN dotnet restore \
+ && dotnet publish -c release -o /app
+WORKDIR /app
+ENTRYPOINT ["dotnet", "service.dll"]