feat: add lerna clean for clean:full and build:full scripts

With loopback-next monorepo, sometimes we have to switch between branches
that have different packages. It becomes problematic to ensure clean states.

This PR adds some scripts to solve the issue:

- npm run clean:full (triggers lerna clean to remove all node_modules)
- npm run build:full (run full clean, lerna bootstrap, build, test, and lint)

package.json

@@ -35,9 +35,10 @@
     "prettier:check": "npm run prettier:cli -- -l",
     "prettier:fix": "npm run prettier:cli -- --write",
     "clean": "lerna run --loglevel=silent clean",
+    "clean:full": "npm run clean && lerna clean --yes --loglevel=silent",
     "build": "lerna run --loglevel=silent build",
     "build:current": "lerna run --loglevel=silent build:current",
-    "build:full": "npm run clean && npm run build && npm run mocha && npm run lint",
+    "build:full": "npm run clean:full && npm run bootstrap && npm run build && npm run mocha && npm run lint",
     "pretest": "npm run clean && npm run build:current",
     "test": "node packages/build/bin/run-nyc npm run mocha",
     "mocha": "node packages/build/bin/select-dist mocha --opts test/mocha.opts \"packages/*/DIST/test/**/*.js\" \"packages/cli/test\"",