feat(exp): add hcloud client mock package

[jooola]

This adds a generated mock for the hcloudmock.Client that will be usable for external library for testing.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 70.54%. Comparing base (a61c494) to head (0f02426).

Files	Patch %	Lines
hcloud/exp/hcloudmock/client.go	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #442      +/-   ##
==========================================
- Coverage   70.91%   70.54%   -0.38%     
==========================================
  Files          35       36       +1     
  Lines        3772     3792      +20     
==========================================
  Hits         2675     2675              
- Misses        688      708      +20     
  Partials      409      409              

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[phm07]

I started implementing the new mocks in the CLI: hetznercloud/cli@4329583
It saves us quite a bit of code there. Although it would be nicer if we had a unified interface that the mock client would implement and also a wrapper for the regular hcloud-go client that has those methods, like we do in the hcapi2 package in the cli.
On a side note, I think the package name mock is a bit too generic and could cause some collisions. I still think it's a very good idea to put this logic into hcloud-go instead of cluttering other integrations with it.

[jooola]

Although it would be nicer if we had a unified interface that the mock client would implement and also a wrapper for the regular hcloud-go client that has those methods, like we do in the hcapi2 package in the cli.

I am not sure to fully understand your suggestions, could you elaborate please?

[jooola]

Implementing a mock for the client will be on hold until we can implement an interface first client. The current struct based client does not allow us to swap the client implementation (real and mock) easily.