feat(datacenter, server-type): move available and recommended to server_type

[phm07]

See:

• https://docs.hetzner.cloud/changelog#2026-04-01-datacenter-deprecations
• feat(datacenter, server_type): move available and recommended to server_type hcloud-go#835

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.64%. Comparing base (c4d60b3) to head (f026121).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1384      +/-   ##
==========================================
+ Coverage   72.62%   72.64%   +0.02%     
==========================================
  Files         300      300              
  Lines       11067    11084      +17     
==========================================
+ Hits         8037     8052      +15     
- Misses       2132     2134       +2     
  Partials      898      898              

Flag	Coverage Δ
e2e	51.25% <0.00%> (-0.09%)	⬇️
unit	67.59% <100.00%> (+0.03%)	⬆️

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