Inconsistent Model Initialization in UnknownIP Model

An inconsistency has been identified in the model initialization within `src/auth-service/models/UnknownIP.js`. The file uses both `getModelByTenant(dbTenant, "UnknownIP", UnknownIPSchema)` and direct mongoose model initialization with `mongoose.model("UnknownIPs")`, which could lead to tenant isolation issues.\n\nPR URL: https://github.com/airqo-platform/AirQo-api/pull/3919\nComment URL: https://github.com/airqo-platform/AirQo-api/pull/3919#discussion_r1857373937\n\nRequested by @Baalmart.