Add zoekt-ci-image

What does this MR do and why?

Needed for gitlab!108937 (merged) which is needed for gitlab!105049 (merged) this MR adds a Dockerfile.zoekt-ci-image to build an image we will use as a services for CI jobs for gitlab-org/gitlab. Zoekt is a new dependency we're adding to GitLab as an optional way to provide a better code search experience. You can read more in the blueprint.

This MR introduces a Dockerfile that builds an image that runs the 2 Zoekt processes needed for our Zoekt dependent tests to run. For now it's installing a fork of Zoekt as the features we need have not yet been upstreamed but that is ultimately our intention at which point we'd start using the main Zoekt repo. Also the fork being used is currently in my personal namespace but I'm happy to move that anywhere once I get a good suggestion of where to move it.

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.