[Feature] - Add Java code-completion for configuration schema

[EddeCCC]

Is your feature request related to a problem? Please describe.
The configuration schema implemented for #1726 just supports code-completion for YAML/JSON. It would be awesome, if we could also get code-completion for actions.

Describe the solution you'd like
Code completion for Java snippets in actions. This probably requires an IDE plugin.

Describe alternatives you've considered
The IntelliJ language injection does not fullfill the requirement in any manner.