netty-all should not re-package jars (netty#11732)

Motivation:

As of today our netty-all artifact does just re-package classes / native libs that are included in our other modules. This can result in all kind of different issues especially if some people have netty-all and other netty-* modules on the classpath.

Modifications:

- Change netty-all to not re-package but just depend on the other different modules
- Use the flatten plugin to ensure the correct dependencies are added to the final pom.xml and the optional dependencies are excluded
- Adjust profiles
- Adjust release scripts

Result:

netty-all does not repackage and just pulls in its dependencies.

Result:

After your change, what will change.

.gitignore

@@ -46,3 +46,6 @@ mainframer
 # exclude vscode files
 .vscode/
 *.factorypath
+
+# exclude file created by the flatten plugin
+.flattened-pom.xml