Migrate secret-detection template to a CI component

Overview

As part of the efforts to build a catalog of CI components, we want to convert all Static Analysis relevant templates to CI components.

The first two have already been converted by @fabiopitino:

• https://gitlab.com/gitlab-components/code-quality
• https://gitlab.com/gitlab-components/sast

But we still have to migrate the secret-detection template to a CI component.

Proposal

Using the instructions outlined in this comment, convert the template to a CI component similar to the above two.