refactor: modernize Makefile build system for new architecture

Update both the root Makefile and .devcontainer/Makefile to support
the new modular architecture:

Root Makefile changes:
- Restructure with clear sections (system, buildtime, versions, naming, runtime)
- Add new image naming: base, cpu, cuda, rocm (replacing old triton-* names)
- Add comprehensive runtime configuration options for all frameworks
- Add support for INSTALL_* variables for modular framework setup
- Add new build targets for base, cpu, cuda, rocm images
- Add new run targets for all framework/variant combinations
- Improve documentation and organization

.devcontainer/Makefile changes:
- Update VARIANTS to use new naming: cpu, cuda, rocm
- Update clean targets for new generated file names

Benefits:
- Clearer organization with well-defined sections
- Support for new modular setup scripts
- More flexible runtime configuration
- Better naming that reflects actual hardware support
- Improved maintainability

This modernization integrates with the new Dockerfiles from PR redhat-et#121
and leverages the modular scripts from PRs redhat-et#115-120.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: cmagina

.devcontainer/Makefile

@@ -1,4 +1,4 @@
-VARIANTS := triton triton-cpu triton-amd
+VARIANTS := cpu cuda rocm
 BASE_DIR := $(CURDIR)
 
 ##@ Devcontainer
@@ -20,12 +20,12 @@ list: ## List all variants
 
 clean: ## Remove all generated devcontainer.json files
 	@for v in $(VARIANTS); do \
-	  echo "Removing $$v/devcontainer.json"; \
-	  rm -f $(BASE_DIR)/$$v/devcontainer.json; \
-	  echo "Removing $$v/user.sh"; \
-	  rm -f $(BASE_DIR)/$$v/user.sh; \
-	  echo "Removing $$v/postStartCommand.sh"; \
-	  rm -f $(BASE_DIR)/$$v/postStartCommand.sh; \
+		echo "Removing $$v/devcontainer.json"; \
+		rm -f $(BASE_DIR)/$$v/devcontainer.json; \
+		echo "Removing $$v/create_user.sh"; \
+		rm -f $(BASE_DIR)/$$v/create_user.sh; \
+		echo "Removing $$v/postStartCommand.sh"; \
+		rm -f $(BASE_DIR)/$$v/postStartCommand.sh; \
 	done
 
 help: ## Show this help message