Add support for the counter entity

[agustusbotti]

Hi, I propose adding support for the "counter" entity. This would allow for the visualization of multiple countdown timers simultaneously, for example, to track the remaining days for several different events or tasks. A specific use case would be displaying the remaining days of use for multiple water filters, each with its own lifespan. This would greatly improve the user experience by providing a clear and concise overview of these countdowns. Thank you.