BLE Tracker should support loading a list of beacons from MQTT

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

I plan on using ESPHome to set up a BLE tracking system, similar to [this](https://www.reddit.com/r/homeautomation/comments/gcgim4/cross_post_im_tracking_my_cats_location_within_my/). Currently, adding a new beacon to be tracked requires flashing a new firmware (USB or OTA).
Beyond tracking a list of beacons from the config file, I think a valuable addition would be to also use a list of MQTT nodes to store additional beacon configs and automatically start tracking new beacons as soon as a new MQTT config node is posted.

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

The current approach is to maintain a series of config files for each probe, with the list of beacons duplicated within each or included through a separate file, and reflash every ESP32 whenever the beacon configuration changes. Updating a config in MQTT to add a new beacon, to be picked up instantly by all of the probes, would provide a much more interactive response.

**Additional context**