[CI] Use localhost URL prefix for DEPLOY_PRIME_URL & some pkg & script updates

[chalin]

• Uses http://localhost as default --baseURL when $DEPLOY_PRIME_URL is unset. This makes is easier to distinguish uses of . vs . in generated pages!
• Drops the :pkg qualifier from update:* script names; and other related script name tweaks
• NPM package updates
  • Switches to the official hugo-extended NPM package, now that it's available
  • Updates netlify-cli, since we might need it soon.
• This PR is in support of:
  • Improved i18n support #4467
  • [zh] English fallback-page canonical link should refer to en section page #4487