Enhance entity status validation and add test coverage for isEntityActive function

As discussed in [PR #3893](https://github.com/airqo-platform/AirQo-api/pull/3893), the `isEntityActive` function requires input validation for the time parameter, test coverage for edge cases, and configuration flexibility for the threshold. Please refer to the comment [here](https://github.com/airqo-platform/AirQo-api/pull/3893#discussion_r1855639946) for more details.\n\n**Original Comment by @Baalmart:**\n> Create a Github issue for this.