Add Docker support and environment configuration

Introduced Dockerfile, .dockerignore, and example environment file for containerization. Added compose.yml for Docker Compose setup and renamed docker-compose.dev.yml to compose.dev.yml. Updated build.gradle.kts for Java 21 and shadow plugin, and improved .gitignore and .gitattributes. Refactored Config.java to reorder ENV initialization.

compose.dev.yml

@@ -0,0 +1,18 @@
+services:
+  couchbase:
+    image: couchbase:community-7.6.2
+    env_file:
+      - .env
+    ports:
+      - "8091-8097:8091-8097"
+      - "9123:9123"
+      - "11207:11207"
+      - "11210:11210"
+      - "11280:11280"
+      - "18091-18097:18091-18097"
+    volumes:
+      - couchbase_data:/opt/couchbase/var
+    restart: unless-stopped
+
+volumes:
+  couchbase_data: