API addition without API version bump (attachment deletion)

Hello, great work getting #1623 resolved, many thanks 🙏

I'm looking forward to getting it integrated into API consumer Iotas and will make changes to make use of the attachment deletion ability. I noticed however that there's no clean way to determine whether attachment deletion exists on the server, beyond say comparing the app version or detecting the specific failure.

Bumping the API version would be ideal.