Auto launch dashboard on docker container

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

I would like to have dashboard autostarted.
Something like:

esphome dashboard /config --port $PORT --username $USERNAME --password $PASSWORD

On top of adding the command to `/entrypoint.sh`, also a new environment variable should be added `PORT` with a default.

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

Creating a launch.sh on /config fix the issue, but autolaunch at each restart/update would be handy.

**Additional context**

USERNAME and PASSWORD variables are already part of the container, thus suggesting the route is tracked.

Start by reviewing /entrypoint.sh and the existing Docker container environment, including the USERNAME and PASSWORD variables mentioned in the issue. Confirm how the dashboard command should be started and what default PORT is expected; done means the dashboard autostarts after container launch and restart without requiring a /config/launch.sh script.

Written by the indexing model from the issue text.