Refer to WorkspaceName instead of ContentStreamId in commands

[bwaidelich]

Currently, most commands (all implementing the RebasableToOtherContentStreamsInterface) refer to the content stream id.
This has several issues:

• Content Stream are mostly an implementation detail. The intention is to commit changes to a workspace
• As a result, the common use case is cumbersome right now (fetch workspace via WorkspaceFinder to determine content stream id, ...)
• When we introduce "command interception" for privilege enforcement (see WIP: FEATURE: Content Repository Privileges #4185 (comment)) it will be harder to determine the allowed content streams for the authenticated user
• To re-apply commands during rebasing, we need to change the CS id currently (createCopyForContentStream()) – by referring to the workspace, we should be able to simply copy the commands
• Lastly, by referring to the workspace, we will be able to implement some retry mechanism when aggregate checks fail due to a changed content stream during publish/rebase (see Potential race condition when publishing nodes leading to lost content #4680 for example)