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 78.26087% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.59%. Comparing base (1d407d0) to head (cc84d4c).

Files with missing lines	Patch %	Lines
internal/cmd/context/list.go	78.26%	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    11009      +20     
==========================================
+ Hits         7975     7992      +17     
- Misses       2125     2127       +2     
- Partials      889      890       +1     

Flag	Coverage Δ
e2e	51.38% <4.34%> (-0.11%)	⬇️
unit	67.60% <78.26%> (+0.03%)	⬆️

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