fix(server): workspace member count is not limited by policies

[rot1024]

• The number of members of workspaces was not limited by policy. It was fixed.
• Fixed workspace to correctly use default policy.

[netlify]

✅ Deploy Preview for reearth-web canceled.

Name	Link
🔨 Latest commit	cce6bed
🔍 Latest deploy log	https://app.netlify.com/sites/reearth-web/deploys/651d4e82183e030008ec4591

[codecov]

Codecov Report

Merging #722 (cce6bed) into main (d8022a4) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #722      +/-   ##
==========================================
- Coverage   26.71%   26.71%   -0.01%     
==========================================
  Files        1573     1573              
  Lines      171408   171423      +15     
  Branches     3898     3898              
==========================================
  Hits        45796    45796              
- Misses     124523   124538      +15     
  Partials     1089     1089              

Flag	Coverage Δ
server	33.78% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
server/internal/usecase/interactor/common.go	8.95% <0.00%> (ø)
server/internal/app/auth_client.go	0.00% <0.00%> (ø)
server/internal/usecase/interactor/policy.go	0.00% <0.00%> (ø)