feat: add `has_id_or_name` to `DomainIdentityMixin`

[jooola]

• Add a method to check if 2 domains are equal (only check for same ID or same name)
• Adds the DomainIdentityMixin to models that were missing it.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.65217% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 92.84%. Comparing base (6651b60) to head (fd5d804).

Files	Patch %	Lines
hcloud/core/domain.py	88.88%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #373 +/- ## ========================================== - Coverage 92.86% 92.84% -0.02% ========================================== Files 65 65 Lines 2872 2881 +9 ========================================== + Hits 2667 2675 +8 - Misses 205 206 +1 ```

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