feat(instance): support scratch volumes in servers

[Codelax]

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Relates OR Closes #0000

Release note for CHANGELOG:

[codecov-commenter]

Codecov Report

Patch coverage: 72.22% and project coverage change: -0.01% ⚠️

Comparison is base (0e50e1e) 75.71% compared to head (cabee25) 75.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3345      +/-   ##
==========================================
- Coverage   75.71%   75.71%   -0.01%     
==========================================
  Files         175      175              
  Lines       39052    39088      +36     
==========================================
+ Hits        29568    29594      +26     
- Misses       8413     8421       +8     
- Partials     1071     1073       +2     

Files Changed	Coverage Δ
...nal/namespaces/instance/v1/custom_server_create.go	80.59% <72.22%> (-0.69%)	⬇️

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