Publish and sync modals UX improvements

Summary

These are our current publish and sync modals (on develop branch):

	Step 1	Step 2	Step 2 Error	Step 3	Step 3 Error	Cancel	Complete
Publish
Sync			-

There are several issues:

• Titles are not consistent, contain user-generated data (a channel name as a title), there are ambiguous questions ("Are you sure?")
• Ambiguous content ("Are you sure you would like to cancel this task?")
• Publish completion message ("Complete" step), which is exactly the same as the publishing in progress message ("Step 3"), in combination with the "Refresh" button, is confusing - I don't know when it's safe to reload the page
• We used to display channel metadata on a publish modal:

The metadata section was temporarily removed in #2997 for two reasons:

(1) Including user-generated data in modal titles is discouraged by the design system
(2) Language, resources count, and size metadata refer to a version that's about to be published, but the version refers to a current version which is confusing and doesn't fit well into new drafts for channel metadata

References

• see https://design-system.learningequality.org/modals/
• a discussion and some new design drafts for channel metadata

Real-life consequences

Consistency and clarity improvements

Start with the modal screenshots in the issue and the referenced design-system modal guidance, then review the linked channel-metadata discussion and drafts. Done means the publish and sync modals have consistent, unambiguous titles and content, clearer completion and cancellation states, and an agreed treatment for channel metadata.