Update release plugin for sonatype

[Siedlerchr]

TODO: add creds to github secrets etc

[koppor]

> Could not get unknown property 'ossrhUsername' for Credentials [username: null] of type org.gradle.internal.credentials.DefaultPasswordCredentials_Decorated.

@Siedlerchr Could you have a look? (Sorry for not having followed up earlier on this)

[Siedlerchr]

I will try to take a look at the next days...
The above state was for doing a release locally.

[koppor]

Background why we dived into this one: We think, we need to rewrite the part of FXML loading due to oracle/graal#7682, which requires to use Stream instead of Path for a "clean" loading from files stored inside an application distribution.