Previously, the frontend would attempt to make real requests to
`https://not-configured/`, which of course failed. I’ve changed the
internal structure to have the lack of a server expressed as a `null`
server. A new `did-bootstrap` browser-level setting has been added to
track if the user clicked “Don’t use a server.”

Finally, I updated the auth logic for methods that call out to the
server to make them consistent and use the early return style which
reduces indentation.

Removing `react-select` and the new autocomplete. This experiment has
failed, so cleaning things up now.

Seems to build fine, will test later.

Depends on server change:
https://github.com/actualbudget/actual-server/pull/168

Enabling the new autocomplete for dev/preview deployments.

This will allow us to spot any more issues there might be before we
release the new autocomplete.

https://github.com/actualbudget/actual/issues/773

Refactored all feature flags to use the new `useFeatureFlag` hook.

Also added a new functionality to this feature flag: ability to define
custom "default" value for a feature flag. This will allow us to enable
the new autocomplete component for everyone using Netlify builds
eventually (need to address some issues before doing so).