Require term param for search/autocomplete

What does this MR do and why?

Related to #421051 (closed)

I saw a Sentry error and was able to recreate it by hitting: https://gitlab.com/search/autocomplete

Small fix to require terms param in the controller and update specs

Screenshots or screen recordings

N/A

How to set up and validate locally

1. hit http://gdk.test:3000/search/autocomplete
2. verify you do not get a 500 error, and that you get param is missing or the value is empty: term

MR acceptance checklist

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