Added Homematic 8 buttons

[noxhirsch]

This adds HomeMatic 8 button switches like HmIP-MOD-RC8 (which is just a PCB where you can add your own buttons)

Blueprint Checklist

• [x] You viewed the README and conformed to the naming conventions
• [x] You ordered the actions as stated in the README action order
• [x] All filenames are lowercase and uses '-' for spaces and not '_' while using {service-name}-{switch-name-or-type}.yaml format
• [x] Images are png
• [x] Image backgrounds are transparent and is cropped to the device boundries
• [x] Images has a maximum width of 800px and maximum height of 500px
• [x] There are no missing buttons or actions
• [x] Your integration/service is running on the latest version
• [x] You have tested your blueprints and made sure each button and action works

Zigbee2MQTT

• [ ] (older devices) You have ensured legacy is off/false for the device in the Z2M devices Settings (specific) page and that your actions matches those with legacy off?

[Sian-Lee-SA]

Everything looks fine, I'll merge and explore the issue you're having as the heights and width are already hard coded based on the image dimensions.