Disable/Change Hologram for Mystery Vault

[expxx]

Is your feature request related to a problem? Please describe.
I'd like to be able to add my own hologram (or display entity) with another plugin for the Mystery Vault, but I can't disable or change the current one.

Describe the solution you'd like
Add an option to disable the hologram for the Mystery Vault, or at least options to change it's text.

Describe alternatives you've considered

Additional context

[yapzhenyie]

Actually there is already an option for user to disable the hologram or modify the hologram content in `mystery boxes yml` file.