feat(primary-ip): make auto_delete attribute optional

[jooola]

The auto_delete attribute is currently required, but we recommend always setting its value to false:

 Setting `auto_delete` to `false` is recommended, because if a server assigned to the managed ip
 is getting deleted, it will also delete the primary IP which will break the terraform state.

This change makes the auto_delete attribute optional, and defaults to false. Simplifying user's configurations and using a recommended default.

https://docs.hetzner.cloud/reference/cloud#tag/primary-ips/create_primary_ip

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.78%. Comparing base (1c22d4d) to head (de1662d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/primaryip/resource.go	66.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1429       +/-   ##
===========================================
- Coverage   72.98%   37.78%   -35.20%     
===========================================
  Files         112      112               
  Lines       12533    12536        +3     
===========================================
- Hits         9147     4737     -4410     
- Misses       2320     7740     +5420     
+ Partials     1066       59     -1007     

Flag	Coverage Δ
e2e	?
unit	37.78% <66.66%> (+<0.01%)	⬆️

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[lukasmetzner]

Little nit on the docs. Otherwise, looks good to me 🚀