Add a configuration to specify the location of quasar variables src/css/quasar.variables.{ext}

[doox911]

It is necessary to implement the possibility of redefining the file path - src/css/quasar.variables.{ext}(https://github.com/quasarframework/quasar/blob/dev/app-vite/lib/cache/module.cssVariables.js ) in quasar.config, so that it can be placed in accordance with the Feature-Sliced Design (FSD architecture, https://feature-sliced.design).

Note: At the moment, changing the path requires using a patch, which is a temporary and inconvenient solution.