feat(exp): add ensure `powerOff` `powerOn` `shutdown` in serverutil

[jooola]

Add server utils to simplify powering on or powering off a server.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 13.46154% with 45 lines in your changes missing coverage. Please review.

Project coverage is 70.70%. Comparing base (5a84dd9) to head (d065018).

Files	Patch %	Lines
hcloud/exp/serverutil/server.go	18.42%	29 Missing and 2 partials :warning:
hcloud/exp/actionutil/actions.go	0.00%	14 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #512      +/-   ##
==========================================
- Coverage   71.46%   70.70%   -0.76%     
==========================================
  Files          46       47       +1     
  Lines        3935     3987      +52     
==========================================
+ Hits         2812     2819       +7     
- Misses        710      753      +43     
- Partials      413      415       +2     

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