Add Dependency List alert components

What does this MR do?

This adds alert components for the Dependency List MVC. It's one of a handful of MRs that will make up the frontend portion of the feature.

This should satisfy the relevant requirements listed in #10075 (closed), #11059 (closed) and #11397 (closed).

These alerts will be shown during the identified edge cases.

This adds a new somewhat generic alert component that for the most part matches the GitLab design spec, but it's local to the dependency list feature. This local implementation is expected to be replaced soon with a generic implementation of alerts, implemented in gitlab-ui. Once that's done, this feature-specific implementation can be removed/swapped out in favour of that. This issue tracks that work.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers