Allow configuring UI server host via an environment variable

[lminaudier]

What was changed

This PR adds a way to configure the UI server bind address / host using an environment variable. Right now you can configure the port using TEMPORAL_UI_PORT but not the host.

Why?

For consistency with the rest of the configuration options and to avoid having to use a configuration file just for one unexposed option.

Checklist

1. Closes

2. How was this tested:

Ran docker build

𝝺 docker build . -t test/ui-server

And checked setting the environment variable changed the output log showing the bind address

𝝺 docker run -it -e TEMPORAL_UI_HOST=127.0.0.1 test/ui-server
2023/06/13 10:27:21 Loading config; env=docker,configDir=config
2023/06/13 10:27:21 Loading config files=[config/docker.yaml]
...
⇨ http server started on 127.0.0.1:8080

3. Any docs updates needed?

Maybe in another repo?

[feedmeapples]

thx for the PR! could you open it here https://github.com/temporalio/ui. UI-server repo at this point just tracks & builds the changes in /ui