Change disabling of search autocomplete

[csutter]

Caution

This requires the following PRs to be merged first, or autocomplete will temporarily stop working:

• Remove GOVUK_DISABLE_SEARCH_AUTOCOMPLETE feature flag govuk_publishing_components#4533
• Remove "disable autocomplete" feature flag finder-frontend#3624
• Remove "disable autocomplete" feature flag frontend#4569

This was previously managed by rendering a different component in every single rendering application (due to the autocomplete functionality being present in the global header).

This changes it to be a single feature flag on search-api-v2 instead that controls whether any results are returned, and changes it to be a positive flag instead.

[kevindew]

Looks good, but would suggest we probably don't want the superfluous ENABLE_AUTOCORRECT env vars and just want the instructions to tell someone to add it.

[csutter]

Looks good, but would suggest we probably don't want the superfluous ENABLE_AUTOCORRECT env vars and just want the instructions to tell someone to add it.

You're right that the app sets a default for the environment variable, so it's not strictly necessary.

But I think it would still be helpful to specify it in the app config, for two reasons:

• as long as the feature flag exists, it makes it more explicit that we want it enabled (especially now that it's a positively named flag)
• it makes it easier to find for someone who urgently needs to turn off autocomplete but is maybe unfamiliar with the app and/or less confident with our Helm set up

Happy to remove it though if you feel strongly about it.

[kevindew]

Nah, not strong opinions on it. Your points are valid so happy to keep it.