Your Question

I want to create a modpack but to do that I need to disable the generation of Oil Fountains in other dimensions, is it possible to do so and how?

To stop the generation of the oil springs in certain dimensions you can take the following steps:
Go to the raw_oil_sphere.json in the worldgen/vein/overworld folder in the gregtech config folder
Add a dimension_filter entry and specify the dimension that you want the fluid springs to spawn in using one of the structures here: https://github.com/GregTechCE/GregTech/wiki/Worldgen-JSON-Syntax#dimension-filter

eg:

  "dimension_filter": [
    "name:the_end"
  ],

Closing this, as the question was answered