Sidebar changes to support Vercel Platforms

[jacqui]

This should not be published until we are ready to roll out the new stack for Vercel Platforms

Relates to https://github.com/news-catalyst/next-tinynewsdemo/issues/1085

This updates the sidebar, on the whole greatly simplifying what it does:

• no more translation tools
• no more choosing a locale
• document api now supports vercel platforms (_sites/[site] syntax)
• document api requests now include ?site=${site} param
• sidebar Admin Tools config form includes new field for this site param (ex: next-tinynewsdemo, blackbygod.org)

To test, use the latest code in the sidebar. Note: this requires a new config variable called "site" that is available in the admin tools!