feat: attach server to a specific network subnet

[jooola]

Allows the users to attach a server to a given network subnet.

Using the subnet_id argument is preferred over the network_id argument.

Closes #650

[codecov]

Codecov Report

❌ Patch coverage is 17.78846% with 342 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.27%. Comparing base (d79720f) to head (b7b2a60).

Files with missing lines	Patch %	Lines
internal/server/resource_network.go	17.90%	266 Missing ⚠️
internal/server/common.go	0.00%	76 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1217       +/-   ##
===========================================
- Coverage   67.69%   32.27%   -35.42%     
===========================================
  Files          81       83        +2     
  Lines       11542    11730      +188     
===========================================
- Hits         7813     3786     -4027     
- Misses       2919     7898     +4979     
+ Partials      810       46      -764     

Flag	Coverage Δ
e2e	?
unit	32.27% <17.78%> (-0.18%)	⬇️

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