chore: Add clean and build:clean scripts (#1659)

Author: JakeSCahill

package.json

@@ -4,7 +4,9 @@
   "description": "Redpanda documentation",
   "license": "ISC",
   "scripts": {
+    "clean": "rm -rf docs .cache",
     "build": "antora --to-dir docs --fetch local-antora-playbook.yml",
+    "build:clean": "npm run clean && npm run build",
     "serve": "wds --node-resolve --open / --watch --root-dir docs --port 5002",
     "start": "cross-env-shell LIVERELOAD=true npx gulp",
     "test-quickstart": "cd tests/setup-tests && npx doc-detective --input ../../modules/get-started/pages/quick-start.adoc -l debug",