Update example build config to produce a cleaner fat jar

[eneufeld]

Fix #139

[ndoschek]

Thanks Eugen, warnings were reduced significantly during the m2 build.
Also the size of the standalone JAR was decreased by ~4MB (from 26.4MB to 22.1MB).

However, the standalone JAR cannot be started anymore:

java -jar org.eclipse.emfcloud.modelserver.example-0.7.0-SNAPSHOT-standalone.jar 
Error: Unable to initialize main class org.eclipse.emfcloud.modelserver.example.ExampleServerLauncher
Caused by: java.lang.NoClassDefFoundError: org/eclipse/emfcloud/modelserver/emf/di/ModelServerModule

Could you have another look there, thanks!

Regarding the GitHub workflow builds: --> Extracted this to a separate issue: #269

It seems that they updated to maven 3.9.0, which has a breaking change regarding the maven.config file we use: https://maven.apache.org/docs/3.9.0/release-notes.html#potentially-breaking-core-changes
To fix this for the newest maven version, we need to split the arguments in separate lines:

.mvn/maven.config:

--settings
./.mvn/custom-settings.xml

I quickly checked with an older version (3.8.6), the adjusted maven.config worked for me locally as well.

[ndoschek]

Why do we remove this lib dependency?

[eneufeld]

it's not needed as it is pulled in by the other dependencies. We get rid of many warnings by removing it.

[ndoschek]

Regarding the GitHub workflow builds: --> Extracted this to a separate issue: #269

Workflows are functional again, after rebasing the checks should work again.