Auto-Focus Group on Creation

[m-peeler]

When a new group is created, it is automatically focused in the viewer. This addresses and closes #11449.

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

Besides minor comments, LGTM 👍. The changes need a second review and thus this PR awaits a second review.

[koppor]

Due to the discussion at #11449 postponed to 6.0-alpha

[koppor]

@m-peeler I needed to merge main and update CHANGELOG.md, because we had a release meanwhile. And due to the discussion at the issue, I did not dare to distribute that functionality in a release.