feat: allow listing contexts as json/yaml

[phm07]

Adds -o=json|yaml to context list. This also fixes hcloud context list --quiet outputting nothing at all.

Fixes #1347

[phm07]

Not sure if we want to expose tokens by default

[codecov]

Codecov Report

❌ Patch coverage is 80.76923% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.59%. Comparing base (1d407d0) to head (cac9104).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/cmd/context/list.go	80.76%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1352      +/-   ##
==========================================
+ Coverage   72.57%   72.59%   +0.02%     
==========================================
  Files         300      300              
  Lines       10989    11028      +39     
==========================================
+ Hits         7975     8006      +31     
- Misses       2125     2130       +5     
- Partials      889      892       +3     

Flag	Coverage Δ
e2e	51.44% <7.69%> (-0.05%)	⬇️
unit	67.52% <80.76%> (-0.05%)	⬇️

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