Error message for missing users and roles in linkahead_admin.py

Summary

Added error messages when retrieving and updating an user or role with linkahead_admin. Addresses #200 (closed)

Focus

The code changes are in the second diff version, the other changes are exclusively indentation fixes for docstrings. Would it be useful to also add success messages for operations that do not print anything?

Check List for the Author

• All automated tests pass
• Reference related issues
• Not necessary: Appropriate user and developer documentation for new code
• Annotations in code

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Appropriate user and developer documentation for new code
• The intended behavior is reproducible

assigned to @i.nueske

added 1 commit

• 794f67a1 - MNT: Added error messages for all user and role updates, unified message layout.

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added 1 commit

• b9c69dcb - STY: Fix broken docstring indentation

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marked the checklist item Annotations in code as completed

changed the description

mentioned in issue #200 (closed)

changed the description

requested review from @florian

marked the checklist item I understand the intent of this MR as completed

marked the checklist item All automated tests pass as completed

added 1 commit

• 78803284 - DOC: Update changeolg

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marked the checklist item Appropriate user and developer documentation for new code as completed

marked the checklist item The intended behavior is reproducible as completed

enabled an automatic merge when all merge checks for 78803284 pass

mentioned in commit eb79cfbd

merged