Use idiomatic go to retrieve user full name

[rafaelsousa]

### Description:

Fixes #(issue)

Checklist:

• [x] Tests included.
• [x] Lint and formatter run with no errors.
• [x] Tests all pass.

Where applicable:

• [ ] Public APIs match existing style.
• [ ] Any breaking changes have a deprecation path or have been discussed.
• [ ] Updated the vendor folder (using go mod vendor).

[coveralls]

Pull Request Test Coverage Report for Build 3884594387

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 29.53%

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Files with Coverage Reduction	New Missed Lines	%
internal/ui/switcher.go	3	82.52%
internal/ui/launcher.go	8	50.36%
<!--	Total:	11		-->

Totals
Change from base Build 3878300944:	-0.2%
Covered Lines:	1532
Relevant Lines:	5188

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💛 - Coveralls

[rafaelsousa]

Is there any POSIX way of knowing that? So far, the only place I could have that information is within /etc/passwd. Or else, I think we get everything before the first space. Ok with that ?

[andydotxyz]

Splitting on space is probably ok for now :).