feat(instance): add server action command

[Codelax]

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Relates OR Closes #0000

Release note for CHANGELOG:

[codecov-commenter]

Codecov Report

Merging #3309 (79131b8) into master (b2aa437) will increase coverage by 0.01%.
Report is 1 commits behind head on master.
The diff coverage is 86.26%.

@@            Coverage Diff             @@
##           master    #3309      +/-   ##
==========================================
+ Coverage   75.62%   75.64%   +0.01%     
==========================================
  Files         171      172       +1     
  Lines       38121    38152      +31     
==========================================
+ Hits        28828    28859      +31     
  Misses       8252     8252              
  Partials     1041     1041              

Files Changed	Coverage Δ
internal/namespaces/instance/v1/custom_server.go	76.74% <ø> (-2.85%)	⬇️
...nal/namespaces/instance/v1/custom_server_action.go	86.22% <86.22%> (ø)
internal/namespaces/instance/v1/custom.go	98.22% <100.00%> (+0.01%)	⬆️