feat(auth): add auto-generation of oauth credentials

Implement functionality to create the oauth_creds.json file from
environment variables (ACCESS_TOKEN, REFRESH_TOKEN, EXPIRY_DATE)
if the file is missing. Also update documentation, docker-compose,
and build scripts to support this new feature.

docker-compose.yml

@@ -0,0 +1,20 @@
+version: '3.8'
+services:
+  gemini-cli-openai-api:
+    container_name: gemini-cli-openai-api  
+    image: sfiorini/gemini-cli-openai-api:latest
+    ports:
+      - "4343:4343"
+    # Enable sharing a pre existing OAuth credentials file
+    # to avoid the need to set environment variables.
+    # volumes:
+    #   - ~/.gemini/oauth_creds.json:/root/.gemini/oauth_creds.json
+    environment:
+      - TZ=America/Chicago
+      - PORT=4343
+      - VERBOSE=false
+      - API_KEY=MY0P3NA1K3Y
+      - ACCESS_TOKEN=MYACC3SS_T0K3N
+      - REFRESH_TOKEN=MYR3FR3SH_T0K3N
+      - EXPIRY_DATE=1234567890
+    restart: unless-stopped