This PR makes the code that selects the client icon in the webui depeding on the uname information
leaner and easier to adapt.

Please check

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Checklist for the reviewer of the PR (will be processed by the Bareos team)

Make sure you check/merge the PR using devtools/pr-tool to have some simple automated checks run and a proper changelog record added.

General

• Is the PR title usable as CHANGELOG entry?
• Purpose of the PR is understood
• Commit descriptions are understandable and well formatted
• Required backport PRs have been created
• Correct milestone is set

Source code quality

• Source code changes are understandable
• Variable and function names are meaningful
• Code comments are correct (logically and spelling)
• Required documentation changes are present and part of the PR