Add AutoDevOps template validation spec

What does this MR do?

Adds an ad-hoc spec for validating AutoDevOps templates.

Rel: gitlab-org/quality/testcases#31, #30939 (closed)

Closes gitlab-org/quality/testcases#762 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content