Added initial implementation of SavedChangesMessages.vue

What does this MR do?

This MR adds the SavedChangesMessages.vue component in preparation for use by the future StaticSiteEditor.vue parent component.

Screenshots

The UI will not render until wired up by a future MR that has the planned StaticSiteEditor.vue parent component. When used, it will render this mockup

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