feat(instance_server): allow root_volume size update

[Codelax]

Closes #2605

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 6.66667% with 28 lines in your changes missing coverage. Please review.

Project coverage is 71.30%. Comparing base (fe86049) to head (87106bc).
Report is 193 commits behind head on master.

Files with missing lines	Patch %	Lines
...ternal/services/instance/helpers_instance_block.go	0.00%	20 Missing ⚠️
internal/services/instance/server.go	20.00%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2745      +/-   ##
==========================================
- Coverage   71.43%   71.30%   -0.13%     
==========================================
  Files         277      328      +51     
  Lines       35875    32919    -2956     
==========================================
- Hits        25628    23474    -2154     
+ Misses       8028     7198     -830     
- Partials     2219     2247      +28     

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