create aspnet api with postgresql

This version added a compose application using:
* ASP.Net API Core
* EntityFramework Core
* Postgresql

Signed-off-by: Eduardo Silva <eduardo.lour.silva@gmail.com>

aspnet-api-postgresql/README.md

@@ -0,0 +1,62 @@
+## Compose sample application: ASP.Net API with Postgresql database
+
+Project Structure
+```
+.
+├── api
+│   ├── appsettings.json
+│   ├── ...
+└── docker-compose.yaml
+```
+[_docker-compose.yaml](docker-compose.yml)
+
+```
+services:
+  api:
+    image: mcr.microsoft.com/dotnet/sdk
+    container_name: "api"
+    ports:
+      - 5000:5000
+    ...
+  db:
+      image: postgres:10.5
+      restart: always
+      ...
+```
+
+The compose file defines an application with two services `api` and `db`. The api service is configured without a Dockerfile and to run using your local volume in `watch` mode.
+
+## Deploy with docker-compose
+
+```
+$ docker-compose up -d
+Pulling db (postgres:10.5)...
+10.5: Pulling from library/postgres
+...
+Status: Downloaded newer image for postgres:10.5
+Pulling api (mcr.microsoft.com/dotnet/sdk:)...
+latest: Pulling from dotnet/sdk
+...
+Status: Downloaded newer image for mcr.microsoft.com/dotnet/sdk:latest
+Creating aspnet-api-postgresql_db_1 ... done
+Creating api                        ... done
+```
+
+## Expected result
+
+```
+$ docker ps
+CONTAINER ID   IMAGE                          COMMAND                  CREATED              STATUS              PORTS                                       NAMES
+48c8a8911cfb   mcr.microsoft.com/dotnet/sdk   "dotnet watch run --…"   About a minute ago   Up About a minute   0.0.0.0:5000->5000/tcp, :::5000->5000/tcp   api
+84082957734e   postgres:10.5                  "docker-entrypoint.s…"   About a minute ago   Up About a minute   0.0.0.0:5432->5432/tcp, :::5432->5432/tcp   aspnet-api-postgresql_db_1
+```
+
+After the application starts, navigate to http://localhost:5000/swagger/index.html in your web browser.
+
+![page](output.png)
+
+Stop and remove the containers
+
+```
+$ docker-compose down
+```