#1968: Launch GUI in background

[laim2003]

This PR fixes #1968

Implemented changes:

• Changed PROCESS_MODE for the maven tool from DEFAULT to BACKGROUND_SILENT. This launches the GUI without blocking the terminal.

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Testing instructions

Please add conscise, understandable instructions on how a reviewer can test/verify the functionality of your contribution here:

1. Create a GUI Commandlet Execution in your IDE
2. Execute it
3. GUI should only show a few log messages, then the output should terminate and the GUI should pop up.

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
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  with internal
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[coveralls]

Coverage Report for CI Build 26650357092

Coverage increased (+0.009%) to 71.097%

Details

• Coverage increased (+0.009%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15710
Covered Lines:	11650
Line Coverage:	74.16%
Relevant Branches:	7004
Covered Branches:	4499
Branch Coverage:	64.23%
Branches in Coverage %:	Yes
Coverage Strength:	3.14 hits per line

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💛 - Coveralls

[laim2003]

Made a little mistake while resolving a merge conflict... will clean this up quickly and then mark it as ready to merge again

[hohwille]

@laim2003 thanks for this PR. Besides running in background you also fixed a bug that you already fixed in PR #1967 and I did not understand it during the review and since time was running out before the release I just reverted your change causing the bug again.
Sorry for that and great that you fixed it again. 👍
Ready for merge.