Implement the generator pattern in places where we handle big list

[artonge]

• [scaling] User list
• [scaling] Iterating user list of a group
• [perf] File list
  • For getChildren/getDirectoryContent merging the subsequent request is hard, especially for mount points with duplicates filenames. Solution would be to store the history of filesname with hash or something else.
  • Not so an issue for big instances as it is mostly one user having a lot of files in one folder.
• [scaling/perf] Add generator in IResult Improve IResult #56494
• Add documentation