Add WebUI port to .env file to be able to change 6052 to, for example, 80.

**Describe the problem you have/What new integration you would like**
I would like to change with an environment variable the standard port 6052 (exposed WebGUI port) to something like 80. I am not using port binds because I run this docker container in a macvlan with its own IP, therefore the port bindings are ignored.

**Please describe your use case for this integration and alternatives you've tried:**
I modified the Dockerfile, but this is inconvenient when I update esphome. I need to manually every time apply this change.

**Additional context**

Start by reviewing the Dockerfile, which the request identifies as the current place requiring manual modification, and trace how the WebUI port 6052 is exposed. The change is complete when an environment variable can select an alternative WebUI port, such as 80, without editing the Dockerfile after updates.

Written by the indexing model from the issue text.