Add clean target for .tiltbuild and charts

Makefile

@@ -945,12 +945,22 @@ set-manifest-image:
 clean: ## Remove all generated files
 	$(MAKE) clean-bin
 	$(MAKE) clean-book
+	$(MAKE) clean-tilt
+	$(MAKE) clean-charts
 
 .PHONY: clean-bin
 clean-bin: ## Remove all generated binaries
 	rm -rf $(BIN_DIR)
 	rm -rf $(TOOLS_BIN_DIR)
 
+.PHONY: clean-tilt
+clean-tilt: ## Remove all files in .tiltbuild
+	rm -rf ./tiltbuild
+
+.PHONY: clean-charts
+clean-charts: ## Remove all local copies of Helm charts in ./hack/observability
+	(for path in "./hack/observability/*"; do rm -rf $$path/charts ; done)
+
 .PHONY: clean-book
 clean-book: ## Remove all generated GitBook files
 	rm -rf ./docs/book/_book