Support Immich URL/API key via docker-compose env vars

docker-compose.yml is tracked in a repo meant for publishing, so it can't
hold a real API key. Renamed it to docker-compose.yml.example (placeholder
values, safe to commit) and gitignored the real docker-compose.yml --
deploying is now "cp the example, fill in real values, docker compose up",
no .env file needed.

config.load() now reads IMMICH_URL/IMMICH_API_KEY from the environment
and applies them on top of whatever's in config.json, so setting them in
the compose file's environment: block takes effect without ever touching
the web UI. Env vars always win over the UI-saved values when both are
present -- verified they survive a save() with different UI-entered
values still in place.

server/docker-compose.yml.example

@@ -0,0 +1,13 @@
+services:
+  espresso-frame-server:
+    image: git.thumeit.com/tfaour/espresso-frame-server:latest
+    build: .
+    ports:
+      - "8420:8420"
+    volumes:
+      - ./data:/data
+    environment:
+      - CONFIG_PATH=/data/config.json
+      - IMMICH_URL=http://your-immich-host:2283
+      - IMMICH_API_KEY=your-immich-api-key-here
+    restart: unless-stopped