chore(make): add a clean target

Removes the artifacts that are produced by the other targets and ignored by git, so a broken state can be reset without
remembering which directories are generated. `helm dependency build` populates `charts`, the readme generator installs
`node_modules` and packaging leaves the chart archive and its signature behind.

Co-authored-by: Copilot <copilot@github.com>

Makefile

@@ -1,5 +1,11 @@
 SHELL := /usr/bin/env bash -O globstar
 
+# CLEAN
+# ==============================================================================
+PHONY+=clean
+clean:
+	-rm -rf charts *.tar.gz *.tar.gz.sig node_modules
+
 # MISSING DOT
 # ==============================================================================
 PHONY+=missing-dot