Update gl-form-fields to support a template based usage

Description

Right now the gl-form-fields only support a configuration-based approach and passing in templates/components is not supported. For readability and ease of use passing in templates/components would be a better approach.

Another example here: https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/7874+

Proposed solution

An approach with slots passing in the necessary options, or a gl-form-field-component be a good solution for this.