Fixed geo-location for devices

**Describe the problem you have/What new integration you would like**

I would like to be able to set a fixed geographic location for my esphome devices.
The location can be hard coded or set with home assistant.
This should allow to show esphome on home assistant map cards or use Prometheus and Grafana to show devices on a map.

**Please describe your use case for this integration and alternatives you've tried:**

If using esphome on large perimeter setups, like farms, large gardens etc. you can select and monitor the devices based on a geographic representation on a map.
An easy to implement solution would be to allow constant values in the GPS module.

**Additional context**

The request names no files, tests, or entry points. Start by locating how ESPHome device configuration and location-related data are represented, then determine how a fixed location could reach Home Assistant, Prometheus, and Grafana. Done means devices can expose a configured geographic position for map-based monitoring.

Written by the indexing model from the issue text.