Add steam boiler support

Signed-off-by: Simon Völcker <simon.voelcker@frequenz.com>

Author: simonvoelcker

RELEASE_NOTES.md

@@ -10,7 +10,7 @@
 
 ## New Features
 
-<!-- Here goes the main new features and examples or instructions on how to use them -->
+Added support for steam boilers.
 
 ## Bug Fixes