make "require subscription" toggleable in build (#6144)

## Summary

Adds build time feature flags system starting with a flag that indicates
whether subscription is required to use the app. This is only used on
cloud.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6144-make-require-subscription-toggleable-in-build-2916d73d3650813bb140c5e96bcce1ce)
by [Unito](https://www.unito.io)

vitest.setup.ts

@@ -9,6 +9,9 @@ globalThis.__ALGOLIA_APP_ID__ = ''
 globalThis.__ALGOLIA_API_KEY__ = ''
 globalThis.__USE_PROD_CONFIG__ = false
 globalThis.__DISTRIBUTION__ = 'localhost'
+globalThis.__BUILD_FLAGS__ = {
+  REQUIRE_SUBSCRIPTION: true
+}
 
 // Mock Worker for extendable-media-recorder
 globalThis.Worker = vi.fn().mockImplementation(() => ({