Veikk A15 has no aux button support

[adhdandy]

Description

I have made the necessary changes to fix the issue for myself, but I don't know how to implement them in a way that would work as a PR for the project without breaking support for other Veikk tablets.
Could someone look at the changes I made in my fork and add them properly?

Fork: https://github.com/adhdandy/OpenTabletDriver

Acknowledgements

• I have searched the existing issues and this new issue is not a duplicate of any.
• I have written a concise and meaningful title.
• I am on the latest version of OpenTabletDriver.

[jamesbt365]

Just submit a parser under a new name and evidence that it works, provide data recordings of movement on both the X and Y axis in your PR alongside pressure if possible.