Better Deployment Documentation

### Issue description

The grails documentation is still very lacking in deployment mechanisms. For example, Grails applications work okay in containers with some basic best practices. This ticket is to improve the deployment related documentation, specifically covering:

1. traditional war style deployment
2. container based deployment - including layered builds to minimize space requirements
3. standalone deployment (jar file)
4. ???

Review the existing Grails documentation and identify the deployment entry points covered today. Document traditional WAR deployment, container-based deployment with layered builds, and standalone JAR deployment, while resolving the unspecified fourth topic; done means these mechanisms and their basic best practices are clearly covered.

Written by the indexing model from the issue text.