feat: allow using custom debug write functions

[jooola]

Allow to configure custom functions to write the request/response debug logs.

[jooola]

We might want to make this configurable, e.g. we have a difference between the terraform logs and our CLI.

Maybe using a logging library is easier?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 74.19355% with 8 lines in your changes missing coverage. Please review.

Project coverage is 71.50%. Comparing base (468234e) to head (99246d1). Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
hcloud/client.go	50.00%	4 Missing :warning:
hcloud/client_handler.go	0.00%	1 Missing and 1 partial :warning:
hcloud/client_handler_debug.go	90.47%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #506      +/-   ##
==========================================
+ Coverage   71.46%   71.50%   +0.04%     
==========================================
  Files          46       46              
  Lines        3935     3959      +24     
==========================================
+ Hits         2812     2831      +19     
- Misses        710      714       +4     
- Partials      413      414       +1     

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[github-actions[bot]]

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