refactor: use generic request for remaining get calls

[jooola]

• Also split the metrics query parameter building into a Validate() error and a values() url.Values functions.

[codecov]

Codecov Report

Attention: Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.90%. Comparing base (fc99d70) to head (0dc6c29).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
hcloud/load_balancer.go	95.00%	1 Missing ⚠️
hcloud/server.go	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #625      +/-   ##
==========================================
- Coverage   70.95%   70.90%   -0.06%     
==========================================
  Files          49       49              
  Lines        4431     4416      -15     
==========================================
- Hits         3144     3131      -13     
+ Misses        955      954       -1     
+ Partials      332      331       -1     

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