Improve implementation and completeness of the CM rest API support for getting all (branch) versions of a document

In CMS-13586 'Create REST method to get versions of a document' the initial ground work has been done. There have been added a set of TODOs to improve. The following must be improved

1. Currently, only the UUID of the workspace unpublished document variant works. Obviously, the UUID can also be a versioned (frozen) document UUID
2. All versions are currently fetched one by one with a separate workflow call. In case of many versions this is quite inefficient, certainly because we can just as well fetch them in one go with jcr version history
3. In case the current workspace node is for the branch being looked at in the CM, include it in the Versions. Currently the workspace version is always missing. That Versions just display all versions including the workspace version does not matter since it is not perse that 'versions' only contain the versions from version history: the workspace is just a version as well