feat: Support short and long usernames in rego

[sbernauer]

Description

Please add a description here. This will become the commit message of the merge request later.

Definition of Done Checklist

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# Reviewer
- [ ] Code contains useful comments
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated
- [ ] Changelog updated

# Acceptance
- [ ] Proper release label has been added

[NickLarsenNZ]

I think that makes sense

[adwk67]

@sbernauer I don't think the HDFS mapper issues calls with long names, but only short ones, so I'm not sure if the groups-for-users will work with what comes from HDFS. Have we tested that?

[NickLarsenNZ]

@adwk67, it looks like it does based on the example payload in the README (hidden in a details block):

[adwk67]

@NickLarsenNZ I mean what comes from here: I think that is just the short name: https://github.com/stackabletech/hdfs-utils/blob/main/src/main/java/tech/stackable/hadoop/StackableGroupMapper.java#L73. I'm probably missing something but I don't see where we resolve that against the UGI.

[NickLarsenNZ]

@adwk67, good point - I didn't consider the Group Mapper code when approving.
@sbernauer, will the Group Mapper code be updated to provide additional context?

[sbernauer]

Well that's a pity... public List<String> getGroups(String user) { only seems to give the shortName and not the full name, making it impossible to return the correct groups in this case if I understood correctly