Migrate subdomain deployments to their own GitHub environment (#590)

## Description:

Migrate subdomain deployments to their own GitHub environment, so that
subdomain deployments do not overwrite other subdomains.

| Before | After |
| --- | --- |
|
![image](https://github.com/user-attachments/assets/53be73ab-a01b-4c01-be4f-6f99d358361d)
|
![image](https://github.com/user-attachments/assets/a30d3673-859a-4dec-bea9-d77dd5fdc9ff)
|

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

fake.neo

---------

Co-authored-by: Scott Anderson <662325+scottanderson@users.noreply.github.com>

deploy.sh

@@ -57,9 +57,6 @@ fi
 if [ -f .env.$ENV ]; then
     echo "Loading $ENV-specific configuration from .env.$ENV file..."
     export $(grep -v '^#' .env.$ENV | xargs)
-else
-    echo "Error: Environment file .env.$ENV not found"
-    exit 1
 fi
 
 if [ "$HOST" == "staging" ]; then
@@ -140,7 +137,6 @@ cat > $REMOTE_UPDATE_PATH/.env << 'EOL'
 GAME_ENV=$ENV
 ENV=$ENV
 HOST=$HOST
-SUBDOMAIN=$SUBDOMAIN
 DOCKER_IMAGE=$DOCKER_IMAGE
 DOCKER_TOKEN=$DOCKER_TOKEN
 ADMIN_TOKEN=$ADMIN_TOKEN
@@ -165,4 +161,4 @@ fi
 print_header "DEPLOYMENT COMPLETED SUCCESSFULLY"
 echo "✅ New version deployed to ${ENV} environment in ${HOST} with subdomain ${SUBDOMAIN}!"
 echo "🌐 Check your server to verify the deployment."
-echo "======================================================="
+echo "======================================================="