[Feature] GQL to remove specific custom fields

[Valkyr-JS]

Is your feature request related to a problem? Please describe.
I'm working on a plugin which uses custom fields heavily to store data. I'd like to provide the abilty for users to wipe all custom fields associated with the plugin

Describe the solution you'd like
The ability to specify performer custom fields to be removed, without affecting others.

Describe alternatives you've considered
Currently the way I have to do it is fetch all custom fields for the performer, filter out the ones associated with the plugin, and then overwrite all custom fields using the full and the filtered custom fields object.

Additional context
If it's of any use, here's the function in my plugin which is doing this - https://github.com/Valkyr-JS/glicko/blob/72e2491e7bee1a1377ac50936be8f7279d10e8d1/src/App.tsx#L548. Specifically this is the line where custom fields start to be filtered - https://github.com/Valkyr-JS/glicko/blob/72e2491e7bee1a1377ac50936be8f7279d10e8d1/src/App.tsx#L617