I'm planning to place all the code based on the new Smartthings platform that I'm using from the old Groovy version.
The SpringBoot based backend can be found here
To enable the custom capabitility it is using:
X:\dev\SmartthingsNew>smartthings capabilities:create
? Capability Name: Wholehouse Fan Speed
? Select an action... Add an attribute
? Attribute Name: speed
? Select an attribute type: string
? Maximum length (default: no max length):
? Add a setter command for this attribute? Yes
? If you want to add a basic command, enter a command name now (or hit enter for none):
(Basic commands are simple commands that set the attribute to a specific value.) setHigh
? Command Value: HIGH
? If you want to add a basic command, enter a command name now (or hit enter for none): setLow
? Command Value: LOW
? If you want to add a basic command, enter a command name now (or hit enter for none):
? Select an action... Finish & Create