feat(gitlab-ci): include mandatory jobs

We recently ran into an issue where a change was merged to ci-templates which broken mandatory jobs. Aside from the knock-on effect for other projects, this broke pipelines in subsequent "fix" MRs which hindered their rapid approval and merging.

In uis/devops/continuous-delivery/security-policy!53, this project was exempted from mandatory jobs and we, instead, include the mandatory job template via include:local to ensure that jobs are run. This has the virtuous side-effect that MRs which fix the mandatory job template will have their pipelines succeed.

Since the mandatory jobs include the SAST-IaC template, remove the explicit inclusion from .gitlab-ci.yml.

Closes #192 (closed)