Upgrade linter + refactor display loops

[jotak]

Upgrading linter showed some potential actual bugs during cleanup / exit, where deferred functions aren't called when something like log.Fatal or os.Exit is called, so I had to move things around to fix that (basically: having functions returning errors in case of doing something Fatal, and dealing with fatality in caller)

[openshift-ci]

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[jotak]

(second commit was sort of related to the linter upgrade, since I had to refactor all those big if/else chains for display loops into switches, I'm thinking it can be refactored even further)

[codecov]

Codecov Report

Attention: Patch coverage is 34.25926% with 71 lines in your changes missing coverage. Please review.

Project coverage is 26.20%. Comparing base (01f00d0) to head (27b52da).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/flow_capture.go	4.44%	42 Missing and 1 partial ⚠️
cmd/packet_capture.go	0.00%	18 Missing ⚠️
cmd/flow_db.go	40.00%	6 Missing ⚠️
e2e/cluster/kind.go	0.00%	3 Missing ⚠️
cmd/root.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #137      +/-   ##
==========================================
+ Coverage   26.00%   26.20%   +0.19%     
==========================================
  Files           8        9       +1     
  Lines        1315     1225      -90     
==========================================
- Hits          342      321      -21     
+ Misses        952      888      -64     
+ Partials       21       16       -5     

Flag	Coverage Δ
unittests	26.20% <34.25%> (+0.19%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cmd/display_loop.go	100.00% <100.00%> (ø)
cmd/root.go	43.13% <0.00%> (-3.16%)	⬇️
e2e/cluster/kind.go	0.00% <0.00%> (ø)
cmd/flow_db.go	51.35% <40.00%> (+1.35%)	⬆️
cmd/packet_capture.go	0.00% <0.00%> (ø)
cmd/flow_capture.go	30.14% <4.44%> (-3.61%)	⬇️

[jotak]

oh I forgot @jpinsonneau you did a similar thing in #105 for looping through display modes :(
my bad, I'll remove that

[openshift-merge-robot]

PR needs rebase.

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