BAEL-4652: Running Spring Boot with PostgreSQL in Docker Compose (#10255)

* Initial commit after Spring Starter Wizard.

* Shortened class names.

* Added Docker files, probably not working, yet.

* Ignoring JAR files.

* Docker files work now.

* Fixed application start-up.

* Creating & querying customer.

* Simplified by removing "files" sub-folder for applicaton JAR file.

* Removed more unnecessary settings.

* Removed last "application.properties" setting since this is part of
the Docker Compose file.

* Final tweaking.

docker/docker-spring-boot-postgres/.gitignore

@@ -0,0 +1,38 @@
+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+
+### Custom exclusions ###
+
+*.jar