bringing slimmelezer-be.yaml up to date

[bollewolle]

• apply past updates made on slimmelezer.yaml to slimmelezer-be.yaml
• adding water_delivered sensor used in Belgium

[blancqua]

Just a thank you from my end, waiting for @zuidwijk to merge this and using your version in attendance.

[Datatekniker]

New lines to be updated !!

Error 1 (Line 19):
OLD: id(dsmr_instance).set_decryption_key(key);
New: id(dsmr_instance).set_decryption_key(key.c_str());
Error 2 (Line 65):
Old: id(dsmr_instance).set_decryption_key(private_key);
New: id(dsmr_instance).set_decryption_key(private_key.c_str());